Three-dimensional image element and optical radar device

ABSTRACT

A three-dimensional image element and an optical radar device that have low cost and are capable of detecting a distance to a measurement object at a close distance before a final result of counting the number of pulses is acquired are realized. A pixel storage element has a plurality of binary counters that integrate the number of electrical pulses at mutually different timings and the reading of data by a signal processing circuit and the integration are able to be performed in parallel.

TECHNICAL FIELD

The present invention relates to a three-dimensional image element andan optical radar device. The invention particularly relates to athree-dimensional image element by which a three-dimensional imagemainly constituted by a two-dimensional image of an object andinformation of a distance to the object is acquired, and an opticalradar device utilizing the same.

BACKGROUND ART

A three-dimensional image has a concept that includes not only a normaltwo-dimensional image such as a photograph but also information of adistance to an object within a field of view, and a three-dimensionalimage sensor has been extremely important for peripheral recognition inautomobiles, robots, and the like in recent years. As a two-dimensionalimage sensor, a CCD (charge coupled device) and a CMOS (complementarymetal oxide semiconductor) imager are spreading and both of them performimaging by converting light intensity into an electric signal by asilicon photodiode. As measurement of distance information with highaccuracy, a method of radiating laser light and measuring a flight time(Time-of-flight) required for the laser light to be reflected by theobject and return therefrom is becoming spread.

A method of radiating laser light to a whole of a field of view includesa scanning type in which a laser beam that is narrowed into a dot shape(refer to NPL 1) or a band shape (refer to PTL 1) is used for scanningwith a mirror or the like and a single-radiation type in which a laserbeam is spread and radiated almost uniformly over a whole of a field ofview, and many scanning types in which high beam intensity is easilyobtained at an object have been developed. The scanning type isexpensive and increased in size because it requires a mechanicalconfiguration for oscillating the beam. On the other hand, thesingle-radiation type is easily reduced in size because it does notrequire a mechanical configuration for scanning, but laser lightintensity at the object is smaller as compared to that of the scanningtype, so that when a distance to the object is long, signal intensitybecomes small and accuracy of distance measurement is lowered.

As to measurement of the flight time, since accuracy of time measurementdirectly leads to distance accuracy, a method of emitting pulse laserlight multiple times, repeatedly measuring a time from light emission tolight reception, constructing a histogram (horizontal axis: time,vertical axis: frequency), and deciding the flight time is used. This isa method called TCSPC (time-correlated single-photon counting). As alight receiving element, a SPAD (single-photon avalanche diode) is used.Such a method requires a large circuit scale in each pixel and is thusnot used in an imager, in which pixels are two-dimensionally arrayed ona large scale, and is mainly used in combination with the scanning type(refer to PTL 2 and NPL 1).

On the other hand, in the single-radiation type, a current of aphotodiode is measured and compared to a determination value to decidethe flight time. There is also a case where the current is accumulatedsequentially in capacitors arranged in time sequence and determinationis performed in accordance with an accumulated amount thereof. Accordingto such a mechanism, a three-dimensional image is formed by single laserradiation, so that simultaneity is secured over a whole of a field ofview as an image is captured upon irradiation of flash light, speakingin a photograph. Greatly different from the scanning type in which atime varies at each of points of the field of view, the “flash light” isreferred (refer to PTL 3 and PTL 4).

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No. 2015-73953(published on Apr. 23, 2015)

PTL 2: U.S. Pat. No. 5,892,575 (Apr. 6, 1999)

PTL 3: U.S. Pat. No. 5,696,577 (Dec. 9, 1997)

PTL 4: U.S. Pat. No. 8,130,367 (Mar. 6, 2012)

Non Patent Literature

NPL 1: IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 49, NO. 1, JANUARY2014, P315-330 “A 0.18-m CMOS SoC for a 100-m-Range 10 Frame/s 20096-Pixel Time of Flight Depth Sensor.” Cristiano Niclass, Member, IEEE,Mineki Soga, Hiroyuki Matsubara, Masaru Ogawa, and Manabu Kaaami,Member, IEEE

SUMMARY OF INVENTION Technical Problem

However, a conventional technique described above has the followingproblems.

Since the single-radiation type enables observation of a whole of afield of view at the same time, there is a great advantage that anobject close to an optical radar device is able to he detected early.However, pulse light is radiated at once, so that intensity of lightradiation at a surface of the object is inevitably reduced. Inparticular, in automotive application, since the optical radar deviceneeds to operate even under midday intense sunlight directly on theequator, a distance to a measurement object is inevitably short ascompared to that of the scanning type. Moreover, according to PTL 3,infrared light with a wavelength of about 1.5 m is used to minimize aneffect of background light during daytime, so that silicon is not usableas a light receiving element and a compound semiconductor of InGaAs orthe like is used. On the other hand, since signal processing isperformed by silicon LSI, an InGaAs photodiode and the silicon LSI needto be layered, resulting in a device which is expensive not only inmaterial but also in process.

On the other hand, in a two-dimensional scanning type in which scanningis performed with pulse light in a dot shape, it is difficult to detectall objects that may be subjected to collision until a whole of a fieldof view is scanned. In addition, in one-dimensional scanning in whichscanning in a horizontal direction is performed with pulse light thathas a band shape extending in a vertical direction, an object on a side(for example, a right end of the field of view) where scanning starts isable to be quickly detected, but an object on an opposite side (forexample, a left end of the field of view) is difficult to be detecteduntil the scanning ends.

Thus, a three-dimensional image element in which functions from lightreception to signal processing are mounted in the same silicon chip andwhich is inexpensive and has a wide measurement range so that a nearbyobject is able to be quickly detected to issue a warning, and an opticalradar device of a single-radiation type using the same are required.

An aspect of the invention aims to achieve a three-dimensional imageelement and an optical radar device that have low cost and are capableof detecting a distance to a measurement object at a short distancebefore a final result of counting the number of pulses is acquired.

Solution to Problem

In order to solve the aforementioned problems, a three-dimensional imageelement according to an aspect of the invention includes: a lightreceiving unit in which pixels each including an avalanche photodiodethat detects light in a Geiger mode are arranged in a two-dimensionalmatrix pattern; a pixel storage element to which an electrical pulse issupplied from each of pixels that constitute a column of the pixels; anda signal processing circuit that reads data accumulated by the pixelstorage element and acquires, for each of the pixels, at least distanceinformation indicating a distance to an object, in which the pixelstorage element has a plurality of binary counters that integrate thenumber of electrical pulses at mutually different timings, and thereading of the data by the signal processing circuit is able to beperformed in parallel with the integration.

In order to solve the aforementioned problems, an optical radar deviceaccording to an aspect of the invention includes: a pulse lightillumination system that has a light emitting element that emits pulselight, an optical scanning unit that performs scanning with the pulselight in a direction parallel to a first, plane, and an opticalconversion unit that converts the pulse light into fan-like pulse lightthat is spread in a direction vertical to the first plane; and animaging optical system that images and projects light, which is from atleast a part of a region where light is radiated from the pulse lightillumination system, onto a light receiving unit of a sensor, whichmeasures at least a distance to an object, through an optical band-passfilter.

Advantageous Effects of invention

According to an aspect, of the invention, it is possible to achieve athree dimensional image element and an optical radar device that havelow cost and are capable of detecting a distance to a measurement objectat a short distance before a final result of counting the number ofpulses is acquired.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view illustrating a configuration of an opticalradar device according to Embodiment 1 of the invention.

FIG. 2 is a schematic view illustrating a configuration of a fan-likelight radiation system that constitutes the optical radar deviceaccording to Embodiment 1 of the invention.

FIG. 3 is a schematic sectional view of a three-dimensional imageelement package that constitutes the optical radar device according toEmbodiment 1 of the invention.

FIG. 4 is a schematic view of a three-dimensional image element thatconstitutes the optical radar device according to Embodiment 1 of theinvention.

FIG. 5 is a schematic view of a surface of a pixel of the threedimensional image element according to Embodiment 1 of the invention.

FIG. 6 is a schematic sectional view of the pixel of the threedimensional image element according to Embodiment 1 of the invention.

FIG. 7 is a schematic circuit diagram of the pixel of thethree-dimensional image element according to Embodiment 1 of theinvention.

FIG. 8 is a schematic view of a pixel storage element and a signalstorage processing unit of the three-dimensional image element,according to Embodiment 1 of the invention.

FIG. 9(a) is a timing chart illustrating a driving timing of the pixelstorage element of the three-dimensional image element according toEmbodiment 1 of the invention and FIG. 9(b) is a waveform diagramillustrating enlarged reflection pulse light.

FIG. 10 is a flowchart illustrating a signal processing procedure of asignal processing circuit of the three dimensional image elementaccording to Embodiment 1 of the invention.

FIG. 11 is a graph illustrating a measurement error and measurementdispersion of the three dimensional image element according toEmbodiment 1 of the invention.

FIG. 12 is a schematic view of a three-dimensional image element thatconstitutes an optical radar device according to Embodiment 3 of theinvention.

FIG. 13 is a schematic view illustrating connection of a pixel, signallines, and pixel storage elements of the three-dimensional image elementaccording to Embodiment 3 of the invention.

FIG. 14 is a flowchart illustrating a signal processing procedure of asignal processing circuit of the three-dimensional image elementaccording to Embodiment 3 of the invention.

FIG. 15 is a schematic view illustrating a configuration of a fan-likelight radiation system that constitutes an optical radar deviceaccording to Embodiment 4 of the invention.

FIG. 16 is a schematic view illustrating a configuration of a lightemitting element and a fan-like light radiation system that constitutean optical radar device according to Embodiment 5 of the invention.

DESCRIPTION OF EMBODIMENTS

Embodiments of the invention will be described with reference to FIGS. 1to 16. Hereinafter, for convenience of description, a component havingthe same function as that of a component described in a specificembodiment will be given the same reference sign and description thereofwill be omitted in some cases. In the following explanation, a casewhere fan-like pulse light that is spread in a horizontal direction isradiated to an object on the premise of a field of view that is wider inthe horizontal direction than in a vertical direction by assumingapplication to a land vehicle, distance measurement or the like isperformed, and the fan-like pulse light is used for scanning in thevertical direction will be described. However, a point according to anaspect of the invention is that the field of view in a rectangular shapeis subjected to measurement in a longitudinal direction in a line at atime, and it is needless to say that application to use (such as a caseof mounting in an air vehicle to perform monitoring in the verticaldirection) in which the field of view in the vertical direction is widerthan the field of view in the horizontal direction is also possible byperforming measurement in a line in the vertical direction with use offan-like pulse light that is spread in the vertical direction.

Embodiment 1

An optical radar device 100 according to Embodiment 1 of the inventionwill be described with reference to FIGS. 1 to 11. The optical radardevice 100 includes a pulse light illumination system 110 that has alight emitting element 122 that emits pulse light, a one-dimensionalscanning device (optical scanning unit) 131 that performs scanning withthe pulse light in a direction parallel to a first plane, and a fan-likebeam generator (optical conversion unit) 132 that converts the pulselight used for scanning by the one-dimensional scanning device 131 intofan-like pulse light 124 that is spread in a direction vertical to thefirst plane, and an imaging optical system 151 that images and projectslight, which is from at least a part of a target field of view (regionwhere light is radiated from the pulse light illumination system) 10,onto a light receiving unit 154 of a three-dimensional image element(sensor) 153, which measures at least a distance to an object 11,through an optical band-pass filter 152. The three-dimensional imageelement 153 includes the light receiving unit 154 in which pixelsPx(i,j) including an avalanche photodiode that detects light in a Geigermode are arranged in a two-dimensional matrix, at least one pixelstorage element Mx(j) that is provided in one-to-one correspondence witha column of the pixels Px(i,j) and supplied with an electrical pulsefrom a corresponding pixel Px(i,j), and a signal processing circuit DSthat reads data accumulated by the pixel storage element Mx(j) andacquires, for each of the pixels Px(i,j), at least distance informationindicating the distance to the object 11. The pixel storage elementMx(j) has a plurality of binary counters BC1 to BCγ that integrate thenumber of electrical pulses described above at different timings, andthe reading of the data by the signal processing circuit DS is able tobe performed in parallel with the integration.

As illustrated in FIG. 1, the optical radar device 100 includes thepulse light illumination system 110 that radiates the fan-like pulselight 124 to the target field of view 10, and a light receiving system140 that receives light from at least a part of the target field of view10. The pulse light illumination system 110 has at least an illuminationsystem power source 120, a light emitting element driving circuit 121,the light emitting element 122, and a fan-like light radiation system123. The illumination system power source 120 supplies electric power tothe light emitting element driving circuit 121. The light emittingelement driving circuit 121 pulse-drives the light emitting element 122.The light emitting element 122 emits pulse light. The fan-like lightradiation system 123 performs one-dimensional scanning in the verticaldirection by using the fan-like pulse light 124 that is spread in thehorizontal direction and thereby illuminates a whole of the target fieldof view 10.

The light receiving system 140 has at least a light receiving systempower source 141, the imaging optical system 151, the optical band-passfilter 152, the three-dimensional image element 153, and a controlcircuit 160. The three-dimensional image element 153 has the lightreceiving unit 154 and a signal storage processing unit 155. The lightreceiving system power source 141 supplies electric power to the lightreceiving system 140. The imaging optical system 151 images and projectslight, which is from at least a part of the target field of view 10,onto the light receiving unit 154 through the optical band-pass filter152. The control circuit 160 controls the three-dimensional imageelement 153 and the pulse light illumination system 110 and communicateswith an external system 400.

(Pulse Light Illumination System 110)

The fan-like pulse light 124 is spread in a fan shape in the horizontaldirection and a spread angle thereof is set as a horizontal radiationangle (spread angle in a fan plane of the fan-like pulse light) θh. Onthe other hand, the spread angle in the vertical direction is small anda beam thickness is set as Δθ (full width at half maximum). Thehorizontal radiation angle θh>>the beam thickness Δθ is provided. Whenthe fan-like pulse light 124 is used for scanning within a verticalradiation angle (scanning angle) θv in the vertical direction, thetarget field of view 10 with the horizontal radiation angle θh that isthe spread angle in the horizontal direction and the vertical radiationangle θv that is tie spread angle in the vertical direction is able tobe sequentially subjected to light radiation. Note that, the horizontalradiation angle θh>the vertical radiation angle θv>the beam thickness Δθis provided. That is, the horizontal radiation angle θh is larger thanthe vertical radiation angle θv and the vertical radiation angle θv islarger than the beam thickness Δθ. Hereinafter, when rays of fan-likepulse light 124 to be radiated at different angles in the verticaldirection need to be distinguished from each other, they are describedas fan-like pulse light 124-1 to fan-like pulse light 124-Ns. Nsindicates a total number of times of scanning in the vertical direction.

The fan-like pulse light 124 is preferably uniform in the target fieldof view 10. However, since detection sensitivity in a place where lightintensity is high is high, in a case where there is a place that needsto be particularly gazed in the target field of view 10, the fan-likepulse light 124 is also able to have light intensity distribution inwhich intensity near the place is increased.

FIG. 2 is a schematic view illustrating a configuration of the fan-likelight radiation system 123 that constitutes the optical radar device100. Note that, in FIG. 2, an X direction, a Y direction, and a Zdirection that are three directions vertical to each other are defined.Any direction in an X-Z plane corresponds to a horizontal direction andthe Y direction corresponds to the vertical direction.

As illustrated in FIG. 2, the fan-like light radiation system 123 has atleast a collimate light generator 130 that shapes light from the lightemitting element 122 into almost parallel spot light 133 (in a Y-Zplane: first plane), a one-dimensional scanning device 131 that performsscanning with the spot light 133 in the vertical direction (Ydirection), and a fan-like beam generator 132 that makes the spot light,a traveling angle of which in the vertical direction is changed by theone-dimensional scanning device 131, spread into a fan shape. When thelight from the light emitting element 122 is laser light, the collimatelight generator 130 includes a collimator lens. The one-dimensionalscanning device 131 is constituted by, for example, a MEMS(microelectromechanical systems) mirror element having a reflectionplane that rotationally moves about one axis (which is set as an X axis)in a horizontal plane (X-Z plane). The fan-like beam generator 132includes, for example, a Powell lens. For example, the spot light 133whose diverging angle is about 1.5 degrees and whose diameter at anentry of the Powell lens with an aperture of 8.9 mm is about 3 mm isformed by the collimate light generator 130 and laser light is used forscanning at ±10 degrees with respect to the horizontal plane by theone-dimensional scanning device 131 constituted by the MEMS mirrorelement. Since the Powell lens radiates the laser light at thehorizontal radiation angle θh=90 degrees and the beam thickness Δθ=1degree, the fan-like pulse light 124 is able to be radiated in a rangewith the horizontal radiation angle θh=90 degrees and the verticalradiation angle θv=20 degrees. The MEMS mirror element is, for example,an electromagnetic type, and changes an angle of a mirror by controllingan amount of a flowing current by the control circuit 160. In anelectrostatic or piezoelectric type, the angle of the mirror is able tobe changed by controlling a voltage applied from the control circuit160. The control circuit 160 performs synchronous control of the angleof the mirror and the light receiving system 140 so that a signal fromthe object 11 irradiated with the fan-like pulse light 124 is able to bedetected. The one-dimensional scanning device 131 may be constituted bya polygon mirror, an optical phased array antenna device, or the likeother than the MEMS mirror element.

The light emitting element 122 is a light source capable of emittingpulse light like a laser or an LED (light emitting diode), andpreferably emitting an infrared ray with a wavelength of about 700 nm to1000 nm. Further, the light emitting element 122 preferably has a narrowlight emission wavelength band and a light emission peak wavelengthwhose temperature fluctuation is reduced, and an infrared laser ispreferable. In particular, the light emitting element 122 is preferablya VCSEL (vertical cavity surface emitting laser) that has a narrow lightemission wavelength band and a light emission peak wavelength whosetemperature fluctuation is reduced. Though not described in FIG. 1, atemperature control circuit that performs temperature control of thelight emitting element 122 may be added to the optical radar device 100in order to suppress the temperature fluctuation of the light emissionpeak wavelength.

The light emitting element driving circuit 121 causes a predeterminedcurrent to flow in the light emitting element 122 at a predeterminedtiming to perform pulse light emission from the light emitting element122. The timing of the light emission by the light emitting element 122is decided by a signal from the control circuit 160. An amount of thecurrent flowing in the light emitting element 122 may be variable andmay be controlled by the control circuit 160. The same is also appliedto a time change of a current by which a light emission time of thepulse light is decided. Here, a full width at half maximum (time) of thepulse light is about 1 nsec to several hundreds nsec. Since pulse lightwith large power of several tens W to several hundreds W is required forthe present use, the light emitting element driving circuit 121generally accumulates electric charges in a capacitor and causes theelectric charges to flow in the light emitting element 122 at once tothereby form short pulse light. Thus, the capacitor and/or a switchingelement may be combined with the light emitting element 122 to form amodule.

The illumination system power source 120 has, in addition to a normallow voltage DC (direct current) power source for a logical circuit, ahigh voltage DC power source of several tens V to charge the capacitor.By controlling an output voltage of the high voltage DC power sourceand/or a charging time of the capacitor, the power of the pulse lightemission is able to be controlled. Further, by controlling a switchingspeed of the switching element, a pulse width is able to be controlled.Such controls are able to be performed through the control circuit 160.

In a case that the optical radar device 100 acquires data of 30 framesevery second, pixel resolution of each of the frames is 0.5 degrees, andthe vertical radiation angle θv is 20 degrees, 40 rays of fan-like pulselight 124-1 to fan-like pulse light 124-40 whose travelling angles inthe vertical direction are different are radiated in one frame, forexample. A time allocated to radiation of fan-like pulse light 124-K is1/1200 second, and in this time, an angle of a reflection plane of theone-dimensional scanning device 131 is changed to a setting value andpulse light is emitted from the light emitting element 122. In a casewhere a pulse light emission frequency is 190 kHz, each fan-like pulselight 124-K radiates 158 (=190,000/30/40) pulses to the object 11.

In a case where setting accuracy of the angle of the reflection plane ofthe one-dimensional scanning device 131 is not high, the beam thicknessΔθ is preferably almost equal to or larger than vertical angleresolution corresponding to one pixel of the light receiving system 140.On the other hand, in a case where the setting accuracy of the angle ofthe reflection plane of the one-dimensional dimensional scanning device131 is high, the beam thickness Δθ is preferably almost equal to orsmaller than the vertical angle resolution of the pixel. For example, ina case where the setting accuracy of the angle of the reflection plane±0.2 degrees with respect to the pixel resolution of 0.5 degrees, it isnecessary that the beam thickness Δθ≥0.9 (=0.5+0.2×2) degrees toreliably radiate the pulse light to a target pixel. When the beamthickness Δθ=1 degree, only almost 50 (=0.5/1.0) % of the pulse lightmay be radiated onto a surface of the object 11 that is projected on thetarget pixel. In a case where the setting accuracy of the angle of thereflection plane is ±0.02 degrees, when the beam thickness Δθ=0.5degrees (pixel resolution), 90 (=(0.5−0.02)10.5) % or more of thefan-like pulse light 124 is able to be radiated onto the surface of theobject 11 that is projected on the target pixel. Though the discussionabove is made by assuming that the surface of the object 11corresponding to the target pixel is almost uniformly irradiated withlight, if nonuniformity of light irradiation is acceptable andincreasing irradiation light amount as much as possible is highpriority, the beam thickness Δθ is preferably reduced as small aspossible. For example, in a case where the setting accuracy of the angleof the reflection plane is ±0.2 degrees, when the beam thickness Δθ=0.5degrees, a minimum radiation amount is 60 (=(0.5−0.2)/0.5) % of thepulse light and is able to be made larger than a case of uniformradiation with the beam thickness Δθ=1 degree. In a case of the beamthickness Δθ=0.05 degrees, even when angle setting is shifted from acenter of the pixel, a beam is not spreading to outside of the pixel, sothat almost 100% of the pulse light is able to be radiated. Accordingly,a size of the beam thickness Δθ varies depending on characteristics ofthe one-dimensional scanning device 131 and a form of radiation to theobject surface, but is decided on the basis of the vertical angleresolution corresponding to one pixel, of the light receiving system140.

An advantage of the optical radar device 100 is that the object 11 islikely to be found by first radiation of a few rays of fan-like pulselight 124 without observing the whole of the target field of view 10.This results from that a longitudinal direction of the target field ofview 10 that has a rectangular shape is able to be observed at the sametime, but from which part (vertical direction) of the target field ofview 10 the observation is to be started and what procedure is to beused to advance scanning vary depending on use. For example, variousmethods, such as a method of simply moving the fan-like pulse light 124from a lowermost part to an uppermost part in the vertical direction, amethod of moving the fan-like pulse light 124 from the uppermost part tothe lowermost part to the contrary, and a method of moving the fan-likepulse light 124 downward from a center part so as to jump over from thelowermost part to the uppermost part and return to the center part, areconsidered. In a case where the optical radar device 100 is applied to aland vehicle or the like, start from the center part or a vicinity ofthe lowermost part is preferable. On land, a case where an obstaclefloats in air is rare and there are overwhelming number of cases wherethe object 11 is a person standing on a street or another vehicle.Accordingly, by detecting the object 11 starting from a road surface ora floor surface, the object 11 is able to be detected most reliably andquickly. In a case where the optical radar device 100 is installed at alow position, even start from the center part achieves a similar effect.In such a case, there is a possibility that the object 11 is able to bedetected only by the fan-like pulse light 124-1. By advancing scanningby the fan-like pulse light 124-2, the fan-like pulse light 124-3, and .. . , the object 11 is able to be detected more reliably. In a case ofperforming two-dimensional scanning with a spot-like beam or a case ofperforming scanning in the horizontal direction by using pulse lightthat is spread in a band shape in a vertical direction, the object 11 atissue is not able to be detected in some cases until scanning of thewhole of the target field of view 10 ends.

On the other hand, in a case of usage for preventing a collision of adrone floating in air, scanning is preferably performed from front in atraveling direction. A scanning procedure is able to be appropriatelyselected depending on use. In a case where the target field of view 10having an elongated rectangular shape is observed and scanning isperformed in a transverse direction, however, by simultaneouslyperforming observation in a longitudinal direction, a possibility thatthe object 11 is found promptly increases. In two-dimensional scanningwith a spot beam, simultaneous observation in the transverse direction,or scanning in the longitudinal direction, there remains a possibilityof failing to find the object 11 unless scanning of the whole of thefield of view 10 is completed.

As described above, since order of scanning with use of the fan-likepulse light 124 varies depending on use, it is preferable that the orderof scanning is stored by the control circuit 160, and on the basis ofthe stored information, the fan-like pulse light 124 is used forscanning, and the three-dimensional image element 153 is driven insynchronization with the scanning. Some scanning procedures may bestored so as to be selectable from the external system 400. Moreover,the scanning procedure may be written in storage of the control circuit.160 from the external system 400. Note that, the storage of the scanningprocedure may be performed by an optical radar component other than thecontrol circuit 160, for example, the three-dimensional image element153. Thereby, it becomes unnecessary to externally control the scanningorder for each frame and control of the optical radar device 100 isfurther facilitated.

(Light Receiving System 140)

The imaging optical system 151 is generally a lens. In accordance with asize of the light receiving unit 154 and a viewing angle FOV, a focaldistance and an F-number are able to be appropriately selected. Theimaging optical system 151 preferably has a high transmittance and asmall aberration at a central wavelength of the optical band-pass filter152 described later. Though FIG. 1 illustrates a lens as the imagingoptical system 151, the imaging optical system 151 may be a reflectiveoptical system other than the lens.

The optical band-pass filter 152 has a transmission band in a band of afixed width with a wavelength peak of the pulse light as a center. Awidth (full width at half maximum of wavelength distribution of thetransmittance) of the transmission band is several nm to several tens nmand is preferably about 10 nm to 20 nm. In general, in a case ofoperation outdoors, an operation temperature range is widened and a peakwavelength of the pulse light changes with temperature, so thatdistribution of the pulse light needs to fall within the transmissionband at least in the operation temperature range. In a case of theVCSEL, a temperature shift of a peak wavelength is about 0.07 nm/degree,a full width at half maximum of a light emission peak is about 1 nm, anda temperature shift of a central wavelength of the transmission hand ofthe optical hand-pass filter 152 is 0.025 nm/degree. Thus, even inconsideration of a temperature zone from 85° C. to −40° C., a relativewavelength shift between the peak wavelength and the central wavelengthof the transmission band is about 5.6 nm and the optical band-passfilter 152 with the transmission band of about 10 nm is usable.

In a case where an interference filter in a flat plate shape that isgenerally used is used as the optical band-pass filter 152, when anincidence angle at which light from the object 11 is incident on asurface of the filter increases from 0 degrees, the central wavelengthof the transmission band shifts to a short wavelength side. Thus, whenthe viewing angle FOV is wide, the interference filter in the flat plateshape may not be able to secure the same transmission wavelength band inthe whole of the target field of view 10. Further, when contactingmoisture or oxygen for a long time, the interference filter in the flatplate shape may be denatured and deteriorated with time and is thuspreferably blocked from outside air. In FIG. 1, at the front of theimaging optical system 151, a hemisphere dome made of resin transparentto an infrared ray is provided as a protection cover 150. The protectioncover 150 protects the light receiving system 140 against outside air.In a case where the protection cover 150 is provided, the opticalband-pass filter 152 is also able to be provided, for example, in asurface of the imaging optical system 151 or an inner surface or aninside of the protection cover 150. In a case where the opticalband-pass filter 152 is provided in the protection cover 150, by settinga size of a diameter of a hemisphere in accordance with a diameter ofthe imaging optical system 151, an almost fixed transmission band isable to be secured for light coming from each direction in the targetfield of view 10. As the diameter of the hemisphere increases, a shiftof the transmission band with respect to light that is converged ontoeach pixel is able to be reduced. However, an outer dimension of theoptical radar device 100 increases, so that an actual size is able to bedecided by trade-off between both of them. In a practical range, thediameter of the hemisphere is preferably five times or more, morepreferably ten times or more of the diameter of the imaging opticalsystem 151. In a case where the optical bands-pass filter 152 as in FIG.1 is provided at the front of the imaging optical system 151, it ispreferable that at least a space therebetween is sealed and filled in anatmosphere in which moisture and oxygen are reduced, in order tosuppress degradation of the filter with time.

FIG. 3 is a schematic sectional view of a package 170 that is athree-dimensional image element package constituting the optical radardevice 100.

In a case where the viewing angle FOV is narrow to such an extent thatthe shift of the transmission band as described above becomesinsignificant so far, the optical band-pass filter 152 is also able tobe attached to an inside of lid glass 171 that constitutes an opticalwindow of the package 170 that seals the three-dimensional image element153. In an atmosphere 172, moisture is preferably removed and oxygen ismore preferably removed. Such removal is performed to preventdegradation of the optical band-pass filter 152 over time. Thus, theatmosphere 172 is preferably at least dried air and is more preferablysealed by nitrogen, argon, helium, or the like. Though not illustratedin FIG. 3, silicon resin through which oxygen and moisture are lesstransmitted is preferably used for bonding the lid glass 171 to thepackage 170.

The optical band-pass filter 152 may be incorporated inside the imagingoptical system 151. The number of optical band-pass filters 152described in FIGS. 1 and 3 is one, but may be multiple. A first opticalband-pass filter may be arranged at the front or the back of the imagingoptical system 151 and a second optical band-pass filter may be arrangedin an inner surface of the lid glass 171 as described above. When thefirs optical band-pass filter is provided, energy of light incident onthe package 170 is able to be reduced and an effect of suppressingtemperature rise is achieved. A transmission band of the first opticalband-pass filter is preferably wider than a transmission band of thesecond optical band-pass filter.

FIG. 4 is a schematic view of the three-dimensional image element 153that constitutes the optical radar device 100.

The light receiving unit 154 and the signal storage processing unit 155of the three-dimensional image element 153 are able to be formed on asilicon substrate. Though the light receiving unit 154 and the signalstorage processing unit 155 are also able to be formed as separatechips, connected by using a vertical via hole, a bump, or the like, andlayered, they are preferably configured on the same silicon substrate ina monolithic manner. In a case of a monolithic configuration, sincethere is no inter-chip connection, lowering of reliability due toconnection deterioration, lowering of accuracy caused by a noiseincrease due to an increase of parasitic capacitance, and further anincrease in manufacturing cost are improved.

Though the light receiving unit 154 is arranged on an upper side and thesignal storage processing unit 155 is arranged on a lower side in FIG. 4for convenience, the light receiving unit 154 may be arranged in acenter part. However, it is not preferable that the light receiving unit154 and the signal storage processing unit 155 are mixed. This isbecause a range where the light receiving unit 154 exists extends andthe imaging optical system 151 and the lid glass 171 are enlarged,resulting in an increase of cost.

The light receiving unit 154 of the three-dimensional image element 153has pixels Px(i,j) arranged in m rows and n columns in a two-dimensionalmatrix, and a light signal from the target field of view 10 is projectedby the imaging optical system 151 onto the two-dimensional matrix of them rows and the n columns. Not all the pixels Px (i,j) are activated at atime. Since the pulse light radiated to the target field of view 10 isthe fan-like pulse light 124, only pixels in a row K corresponding tothe fan-like pulse light 124-K are activated. For convenience, thefan-like pulse light 124 is numbered from 1 to Ns (=M) from a lowermostpart to an uppermost part and i of a corresponding pixel Px(i,j) isnumbered from 1 to M from an uppermost part to a lowermost part. Suchcorrespondence is appeared because their orders are reversed to eachother via the imaging optical system 151. This is able to be changeddepending on a property of the imaging optical system 151. That is, whenthe fan-like pulse light 124-K is radiated, a pixel Px(K,j) isactivated. The activation of the pixel Px(K,j) means that an outputsignal of at least the pixel Px(K,j) is transmitted to the signalstorage processing unit 155. Further, power supply to another pixelPx(i,j) may be stopped so that electric power is supplied only to thepixel Px(K,j).

As a circuit by which the pixel Px(K,j) of the row K corresponding tothe fan-like pulse light 124-K is selected, a row selection circuit 161is provided in the light receiving unit 154. Further, a row selectionline R(i) that transmits a signal of the row selection circuit 161 toeach of the pixels Px(i,j) is provided. The row selection line R(i) isnot limited to a single signal line and may be a plurality of signallines that are different in polarity and/or voltage. In synchronizationwith an operation of the one-dimensional scanning device 131 of thefan-like light radiation system 123, the row selection circuit 161selects the row K to be activated. A signal for synchronization isgenerated from the control circuit 160. The row selection circuit 161may control a row selection switch 201 (refer to FIG. 7) of the pixelsPx(i,j), for example, so that only an output of each of pixels Px(K,j)(j=1 to N) is supplied to a signal line Lx(j) or may control a switch(not illustrated) so that power supply voltages VSPAD and Vcc aresupplied only to each of the pixels Px(K,j) (j=1 to N) (refer to FIG.7). Both of the controls may be performed.

The signal storage processing unit 155 has at least one pixel storageelement Mx(j) corresponding to each column j and the pixel storageelement Mx(j) is connected by the respective pixels Px(i,j) and thesignal line Lx(j). Each time a photon is received by the pixel Px(K,j),a signal is transmitted to the pixel storage element Mx(j) through thesignal line Lx(j) and stored. The signal storage processing unit 155further has a buffer memory Bx(j), a column signal line C(j), and asignal processing circuit DS. Data accumulated in the pixel storageelement Mx(j) is copied to the buffer memory Bx(j) through the columnsignal line C(j) at a defined timing. The signal processing circuit DScalculates and outputs at least distance information D (K,j) indicatinga distance to the object 11, two-dimensional image information G1(K,j),and two-dimensional image information G2(K,j) on the basis ofinformation of the buffer memory Bx(j). The two-dimensional imageinformation G1(i,j) and the two-dimensional image information G2(i,j)are respectively able to be two-dimensional image information bybackground light and two-dimensional image information by reflectionlight of the pulse light, but are not limited thereto. The signalstorage processing unit 155 may have a memory selection circuit 163 anda memory selection line Rm(α) that are used to select an a part (binarycounter BCα described later) of the pixel storage element Mx(j). In acase where the pixel storage element Mx(j) outputs a signal to thecolumn signal line C(j), when all outputs are output in parallel, alarge amount of wires are required. Therefore, by reading the signal foreach binary counter BCα constituting the pixel storage element. Mx(j),the number of wires is able to be reduced. In an allowable range of thenumber of wires, signals of a plurality of binary counters may be outputin parallel.

In the signal storage processing unit 155, reading of the signal fromthe pixel storage element Mx(j) and accumulation of the signal in thepixel storage element Mx(j) are able to be performed in parallel. As aresult, a pixel Px(i,j) having high signal intensity is able to bedetected early. In general, the pixel Px(i,j) having high signalintensity captures a closer object 11, thus making it possible to detectthe close object 11 early and issue an alarm. Moreover, any order ofreading of the pixel storage element Mx(1) is able to be selected.

(Light Receiving Unit 154)

FIG. 5 is a schematic view of a surface of a pixel Px(i,j) of thethree-dimensional image element 153. FIG. 6 is a schematic sectionalview of the pixel Px(i,j) of the three-dimensional image element 153.FIG. 7 is a schematic circuit diagram of the pixel Px(i,j) of thethree-dimensional image element 153.

The light receiving unit 154 has the pixels Px(i,j) arranged in atwo-dimensional matrix of in m rows and n columns. As illustrated inFIG. 5, the pixel Px(i,j) is constituted by one or more SPADs(Single-Photon-Avalanche-diodes) 180. Each of the SPADs 180 has a microlens 181 as illustrated in FIG. 6. A structure of the SPAD 180 may havevarious forms, but details thereof will not be given here.

The SPAD 180 has a configuration in which a p⁺ diffusion layer 184 isformed on a surface of an n-type diffusion layer 185 formed on a siliconsubstrate 183. A surface of the silicon substrate 183 is covered with ametal shield 182 at a predetermined interval. The metal shield 182 hasan opening 182 a that is formed so as to expose a part of the p⁺diffusion layer 184. The opening 182 a forms an effective lightreceiving region so that light incident through the micro lens 181passes through the p⁺ diffusion layer 184.

Here, each of the SPADs 180 is described as a PD(a) (a=1 to Nspad,Nspad: total number of SPADs 180 belonging to one pixel). In FIG. 5,except for lower right of a pixel part in which a circuit such as anoutput circuit is arranged, the SPADs 180 are arranged at an almostequal distance. This is because light with a range as wide as possibleis converged by using the micro lens 181 to increase detectionsensitivity. However, as long as the sensitivity is sufficient and apixel area is able to be reduced from a viewpoint of circuit layout, therespective SPADs 180 may be concentratedly arranged in a fixed range. Anoptimum value of Nspad changes depending on the number of photons Mdreceived by one pixel during a deadtime Td of a SPAD 180 that is used.The deadtime Td is a time required for one SPAD 180 to detect a photonand to be then ready to detect a next photon, and has a length of thetime during which the SPAD 180 does not function as a sensor, literally.The deadtime Td generally has a length of about several nsec to 100nsec. When the number of photons Md<<1, Nspad may be small or Nspad maybe 1. When a case where the number of photons Md exceeds 1 can occur,however, if the number of SPADs 180 is one, a period of a next deadtimeTd is not able to be measured at a stage where the first one is counted,so that an upper limit of the countable number of photons is 1 and acorrect number of photons that are received is not able to be measured.Thus, when the number of photons Md is close to 1 or when the number ofphotons Md is larger than 1, Nspad needs to be increased. When a fillfactor (a ratio of a total area of an effective light receiving regionrelative to a pixel area) is the same, detection sensitivity is enhancedas Nspad increases.

An example of a circuit configuration of a pixel Px(i,j) is illustratedin FIG. 7. The pixel Px(i,j) has a SPAD control unit 190 and a photondetection signal generation unit 191 as a part belonging to each of theSPADs 180. The SPAD control unit 190 is a circuit that supplies electricpower to the SPAD 180, and when detecting a photon, performs quenchingand restores a state to a measurement state after the deadtime Td.Though the SPAD control unit 190 in FIG. 7 is illustrated briefly by acircuit in which one resistor is added in addition to the SPAD 180 byassuming passive quenching, an active quenching circuit may be used.Further, it is also possible to add various circuits such as a circuitthat controls activation of the SPAD 180. The photon detection signalgeneration unit 191 is a circuit that, when the SPAD 180 detects aphoton, detects a rise of a terminal voltage of the SPAD 180 and outputsone pulse having a fixed width. FIG. 7 illustrates an example in whichthe photon detection signal generation unit 191 is constituted by afirst inverter 192, a delay circuit 194, a second inverter 193, and aNOR circuit 195. The delay circuit 194 is illustrated by two-stageinverters in FIG. 7, but may be multiple-stage (even number of)inverters or a delay circuit having another configuration. A delay timeof the delay circuit 194 decides a pulse width. The delay time ispreferably from about 0.1 nsec to about several nsec.

Each of the pixels Px(i,j) has a pixel signal output circuit 196. Thisis a circuit that receives a photon detection signal from each of theSPADs 180 in parallel and transmits a pulse having almost the samelength as that of the photon detection signal to the signal line Lx(j).Note that, the pixel signal output circuit 196 is connected to thesignal line Lx(j) through the row selection switch 201. Only the rowselection switch 201 of the row K selected by the row selection circuit161 is turned on by a signal from a row selection line R(K) and rowselection switches 201 of the other rows are turned off. Such a statecontinues while the row K is selected.

In a case where a plurality of SPADs 180 generate photon detectionsignals at almost the same time, the pixel signal output circuit 196 isnot able to distinguish the signals, but is able to reduce an electricalpulse width passing through the signal line Lx(j) as short as possiblein order to minimize such a case. The pixel signal output circuit 196 isconstituted by a signal line driving circuit 197, a signal line resetcircuit 198, and a delay circuit 199 in FIG. 7, but is not limitedthereto. The signal line driving circuit 197 is a circuit that suppliesa current to the signal line Lx(j) upon reception of the photondetection signals and raises potential thereof, and operates completelyin parallel with the respective photon detection signals. In FIG. 7, thesignal line driving circuit 197 has a configuration in which NMOStransistors that receive an output from each of photon detection signalgeneration units 191 by a gate are arrayed in parallel, but may haveanother configuration. For example, a configuration in which the outputfrom each of the photon detection signal generation units 191 isreceived by an AND circuit and one NMOS transistor having high drivingcapability is turned on by an output of the AND circuit may be provided.

The signal line driving circuit 197 needs to have capability of drivingthe signal line Lx(j) with a short signal delay time and transmit asignal to the pixel storage element Mx(j). The delay time is decided bythe driving capability of the NMOS transistor of the signal line drivingcircuit 197 with respect to parasitic capacitance of the signal lineLx(j). The delay time is preferably on a level almost the same as orless than at least the pulse width generated by the photon detectionsignal generation unit 191. In order to reduce the electrical pulsewidth passing through the signal line Lx(j) as short as possible, thesignal delay time in the signal line Lx(j) is preferably short and thesignal line Lx(j) is preferably short.

The signal line reset circuit 198 is a circuit that returns thepotential of the signal line Lx(j), which has been raised by the signalline driving circuit 197, to original potential, and is constituted hereby the delay circuit 199 that delays the signal of the signal line Lx(j)and a signal line pull-down circuit 200, but may have anotherconfiguration. After the potential of the signal line Lx(j) rises andthe pixel storage element Mx(j) reacts, in order to promptly reduce thepotential, the signal line pull-down circuit 200 causes the signal lineLx(j) to ground at a ground level and drops the potential after thedelay time of the delay circuit 199. The delay circuit 199 isillustrated by two-stage inverter chains, but may be inverter chainswith an even number of two or more stages or may be another delaycircuit.

Though the photon detection signal is a pulse that rises from a groundlevel to a Vcc level in FIG. 7, a similar function is able to beachieved even by a pulse that drops from the Vcc level to the groundlevel. Further, though the pulse width of the signal passing through thesignal line Lx(j) is almost decided by the photon detection signalgeneration unit 191 in the configuration of FIG. 7, a configuration inwhich the pulse width is decided by the pixel signal output circuit 196may be provided. The signal line Lx(j) is indicated by one wire in FIG.7, but may have a plurality of wires. For example, with a circuitconfiguration in which two wires are paired and a potential differenceis generated therebetween by the pixel signal output circuit 196 withthe photon detection signal, a signal line may transmit the potentialdifference between the paired wires. In addition, when Nspad is large,the pixel signal output circuit 196 may be divided into a plurality ofcircuits each of which is provided with a signal line.

(Pixel Storage Element Mx(j))

FIG. 8 is a schematic view of the pixel storage element Mx(1) and thesignal storage processing unit 155 of the three-dimensional imageelement 153. FIG. 9(a) is a timing chart illustrating a driving timingof the pixel storage element Mx(j) of the three-dimensional imageelement 153. FIG. 9(b) is a waveform diagram illustrating enlargedreflection pulse light.

In an example illustrated in FIG. 8, the pixel storage element Mx(j) hasat least the plurality of binary counters BC1 to BCγ, a time switch 210by which the signal line Lx(j) is selectively connected to the binarycounters BC1 to BCγ, and an output switch 211 that, upon selection bythe memory selection circuit 163, supplies an output of the binarycounter BCα to the column signal line C(j). The time switch 210 isconstituted by switches S1 to Sγ that are NMOS transistors in FIG. 8.The output switch 211 is constituted by an NMOS transistor in which thememory selection line Rm(α) is a gate input. The binary counter BCα isconnected to the signal line Lx(j) in a time ΔTα during which a switchSα is turned on, and integrates the number of pulses transmitted fromthe pixels (i,j). The number of output bits gα of the binary counter BCαis decided by a maximum value of the number of photons that is counted.Also during the integration by the binary counter BCα, an output of thebinary counter BCα is able to be read out to the buffer memory Bx(j)through the output switch 211.

Signals T1 to Tγ that drive the time switch 210 are signals by which theswitches S1 to Sγ are sequentially turned on in time sequence asillustrated in FIG. 9. In FIG. 9, the pulse width of pulse light andtime widths ΔT1 to ΔTγ (series of time sections continuously arranged intime sequence) in which the switches S1 to Sγ are turned on are equal toa full width at half maximum ΔT of the pulse light, but there is nolimitation thereto. Here, the switch S1 is turned on before emission ofthe pulse light, so that the binary counter BC1 measures intensity ofbackground light. Thus, a time width ΔT1 in which the switch S1 isturned on does not need to be necessarily the same as a time width ΔTαthat is an on-time of another switch Sα. For example, when the timewidth ΔT1 in which the switch S1 is turned on has a length multipletimes of the time in which another switch Sα is turned on, a noise levelof the binary counter BC1 is able to be reduced. In such a case, anoperation of performing division by a multiple by which the length ofthe on-time is lengthened as compared to that of another switch Sα andperforming conversion into data with the same time length as that ofanother binary counter BCα by the signal processing circuit DS increasesonly for the binary counter BC1. The time widths ΔT2 to ΔTγ arepreferably almost the same as or shorter than the full width at halfmaximum ΔT of the pulse light, and when being longer to the contrary, aneffect of the background light increases and an SN ratio of a signal isreduced. For example, in a case where the time widths ΔT2 to ΔTγ have alength twice of the full width at half maximum ΔT of the pulse light, abackground light measurement time becomes twice of a time during whichreflection light of the pulse light may be detected. Thus, an intensityratio of the reflection light of the pulse light to be detected to thebackground light is ½ as compared to that of a case where the timewidths ΔT2 to ΔTγ are almost the same as the full width at half maximumΔT of the pulse light. Accordingly, detection sensitivity for the object11 which is remote and whose reflection light of the pulse light is weakwith respect to the background light is deteriorated.

Since the switch S2 described later is turned on at the same time withlight emission of the pulse light, the binary counter BC2 receives thepulse light that is reflected in an extremely short time. That is, in acase where the object 11 is at a position very close to thethree-dimensional image element 153, a count number of the binarycounter BC2 is increased compared to that of the binary counter BC1.When a distance between the object 11 and the three-dimensional imageelement 153 is a distance L, reflection light of the pulse light reachesthe three-dimensional image element 153 after 2L/c (c: light speed).Thus, corresponding one or two binary counters (binary counters BC3 andBC4 in an example of FIG. 9(a)) receive light with signal intensityhigher than that of the background light.

The foregoing integration is performed throughout the plurality of raysof fan-like pulse light 124-K that are generated over a period duringwhich the row K is selected (for example, 1/1200 sec). That is, a seriesof integrated values arranged in time sequence acquired by thethree-dimensional image element every multiple times of pulse lightradiation is integrated with each other. At a time of end in each row,data accumulated in each of binary counters BCα is read out to thebuffer memory Bx(j). Subsequently, a resent signal Rf is activated andthe previous count number is cleared, so that measurement for a next rowis ready to start.

Here, a total number γ of binary counters BC1 to BCγ has the followingrelation with a maximum measurement distance Dmax and the full width athalf maximum ΔT of the pulse light.

Dmax<(γ−2)·c·ΔT/2

Here, a reason why the formula does not use an equal sign will bedescribed in a next example. Considered is a case of Dmax=30 m, ΔT=100nsec, and γ=4. A reflection pulse from the object 11 at a distance of 30m is counted by the binary counter BC4. However, even when a valuethereof is significantly larger than that of the binary counter BC1, itis not possible to determine that the distance to the object 11 is 30 mas long as a value of the binary counter BC5 is almost equal to that ofthe binary counter BC1, so that a measurement result indicating that thedistance to the object 11 is 30 m is not obtained. On the other hand,when the distance to the object 11 is less than 30 m, a value of thebinary counter BC3 is significantly larger than the value of the binarycounter BC1 and distance measurement may be enabled from the binarycounter BC3 and the binary counter BC4, so that measurement is able tobe performed.

By reducing the full width at half maximum ΔT of the pulse light andincreasing the total number γ of binary counters BC1 to BCγ, distancemeasurement accuracy is able to be improved. In particular, by detectinga plurality of peaks, multiple reflection may be detected or a lighttransmitting object and the object 11 at a position on a deep sidethereof may be detected at the same time. On the other hand, when thetotal number γ of binary counters BC1 to BCγ increases, an area of thepixel storage element Mx(j) increases, which leads to an increase of achip area and an increase of cost. However, since the pixel storageelement Mx(j) and the signal processing circuit DS are basically logiccircuits, by adopting a silicon LSI manufacturing process being furtherminiaturized, an area is able to be reduced. Since manufacturing costfor such a miniaturization process is reduced year by year, the totalnumber γ of binary counters BC1 to BCγ may increase from several tens toseveral hundreds in the future.

As illustrated in FIG. 9(a), it is necessary that the signals T1 to Tγare not overlapped with each other in principle, cover a time zone formeasurement without leakage, and have equal pulse widths to beactivated. However, since the signals T1 to Tγ need to be distributed toall pixel storage elements Mx(j), a slight difference may be caused in awire delay or the like due to a variation of a delay between wires orthe like. Since a difference of the activated pulse widths of thesignals T1 to Tγ directly leads to accuracy of a measurement value ofthe distance, it is necessary to adopt a circuit configuration and/orwire arrangement having high time accuracy in accordance with requiredaccuracy of the optical radar device 100.

The time switch 210 is constituted by the switches S1 to Sγ that aredirectly turned on/off by the signals T1 to Tγ in the example of FIG. 8,but may be constituted by another circuit. For example, a configurationin which outputs of a simple shift resistor (number of bits; γ) aresupplied to the switches S1 to Sγ and an on-state is sequentiallyshifted by a clock signal may be provided. This makes it possible notonly to reduce the number of signals but also to reliably turn on onlyone of the switches S1 to Sγ, resulting that, between switches Sα andS(α+1) which are turned on in adjacent time zones, generation of a gapor overlap between the time zones in which the switches are turned on isprevented and a counting error is able to be reduced. The time switch210 may have any configuration as long as being such a circuit in whichthere is less gap or overlap of the on-time between adjacent switches.

In the foregoing description, a reason why the binary counter BCα isselected as a circuit that counts a pulse signal, which is generatedwhen the light receiving unit 154 detects a photon, in time sequence isthat the binary counter BCα is able to be constituted by a relativelysimple circuit, and when being constituted as an integrated circuit, isable to achieve a function of count and integration with a small area.The reason is also that the binary counter BCα is a simple logic circuitso that a wide operation margin is easily obtained and design is simple.Though the binary counter has such an advantage, the pixel storageelement Mx(j) does not need to be necessarily constituted by theplurality of binary counters BC1 to BCγ. Another configuration is alsopossible as long as being a circuit that, in combination with the timeswitch 210, integrates and stores the detected number of photons everyseries of time sections almost continuously arranged in time sequence.Moreover, it is preferable that a halfway result of integration is ableto be read during integration without greatly affecting an integrationoperation.

(Buffer Memory Bx(j))

It is also possible that the signal processing circuit DS directlyaccesses the pixel storage element Mx(j) and extracts distanceinformation or the like by a method described later from photon countdata being integrated. When the pixel storage element Mx(j) issequentially subjected to reading for processing, however, a great timedifference is caused between a processing timing of a pixel storageelement Mx(1) and a processing timing of a pixel storage element Mx(N)and detection sensitivity may vary. A memory in which information of thepixel storage element Mx(j) is copied and held in order to suppress sucha time difference to the minimum is the buffer memory Bx(j). Wheninformation of the pixel storage element Mx(j) is copied to the buffermemory Bx(j) all at once and the signal processing circuit DS performssignal processing on the basis of data of the buffer memory Bx(j), it ispossible to secure simultaneity of data and achieve uniform detectionsensitivity between pixels in a row.

(Signal Processing Circuit DS)

A function of the signal processing circuit DS will be described on thebasis of the example of FIG. 9(a). When a pulse count number of each ofthe binary counters BCα for data of the pixel storage element Mx(j),which is copied to the buffer memory Bx(j), at a certain time t isNCα(t) (a group of series of integrated values arranged in timesequence), a count number NC1(t), a count number NC2(t), and a countnumber NC5(t) indicate almost equal values except for noise andrepresent intensity of the background light in the example of FIG. 9(a).On the other hand, a count number NC3(t) and a count number NC4(t)include reflection light of the pulse light and are significantly largerthan the count number NC1(t), the count number NC2(t), and the countnumber NC5(t). As a result, the distance to the object 11 is calculatedby the following formula.

D(t)=c·ΔT·[1+{NC4(t)−NC1(t)}/{NC3(t)+NC4(t)−2·NC1(t)}]/2

Here, a meaning of the formula will be described with reference to FIG.9(b). “1” in [ ] is a numeral obtained by dividing a time period Ta, apart of time until the reflection light of the pulse light is incident,by the full width at half maximum ΔT of the pulse light. That is, thenumeral indicates a part corresponding to an integral multiple of thefull width at half maximum ΔT in the time from when radiation of thepulse light starts to when reflection light thereof is incident(accuracy with the same length as the time section), and is “1” in theexample illustrated in FIG. 9(b). Here, the numeral is an integer equalto or more than 0, and when the object is at a long distance, theinteger increases, and when the object is at a short distance, theinteger decreases. A part other than an integer in [ ] corresponds to atime period Tb (accuracy shorter than the time section). That is, avalue obtained by dividing the time period Tb by the full width at halfmaximum ΔT is equal to a value obtained by dividing B (=NC4(t)−NC1(t))by a sum of A (=NC3(t)−NC1(t)) and B in the figure. Thus, a length ofthe time period Tb is ΔT·B/(A+B) Here, A is an integrated value ofreflection pulse light intensity measured during a timing T3 and B is anintegrated value of reflection pulse light intensity measured during atiming T4. Since the pulse width of the pulse light and a time lengthfor measurement are the same, the reflection light is detected in atmost only two adjacent sections as illustrated in FIG. 9(b).Accordingly, a length of the time period Tb is calculated similarly fromthe intensity of the reflection light of the pulse light regardless ofthe distance to the object. Moreover, a reason why the formula isdivided by 2 is that light reciprocates to the object 11 in a timeperiod that is a sum of the time period Ta and the time period Tb, sothat the formula needs to be divided by 2 to perform conversion into thedistance to the object 11.

The signal processing circuit DS is able to output a distance signalD(t) as a distance signal D(i,j) to each of the pixels Px(i,j). As thetwo-dimensional image information G1(i,j) and G2(i,j), the followingsare able to be output.

Background light signal: G1(i,j)=NC1(t)

Pulse light reflection light signal:G2(i,j)=IC(t)=NC3(t)+NC4(t)−2·NC1(t)

In this manner, in the invention, in the count numbers NCα(t) of apulse, an integrated value larger than a noise level is obtained and apair of the larger integrated value and an integral value temporallyadjacent thereto is obtained, so that a distance to the object is ableto be calculated from the count numbers with accuracy shorter than thetime section. With a method of simply deciding a flight time from a timezone indicating a maximum value of NCα(t) like TCSPC, the flight time isable to be decided only with accuracy of c·ΔT/2. (Integer part in [ ] ofD(t)) Thus, in a case of a method such as TCSPC, in order to increaseaccuracy of measurement of the flight time, it is necessary to reduce ΔTand increase the number of NCα(t). This increases a circuit scale, sothat an area of the signal storage processing unit 155 increases andcost increases. According to the present method, however, even when ΔTis reduced, the flight time with accuracy of c·ΔT/2 or less is able tobe decided by using a plurality of NCα(t) temporally adjacent to eachother (part other than an integer in [ ] of D(t)) and accuracy ofmeasurement of the distance to the object is able to be enhanced.

Though an output signal is measured basically along an idea as describedabove, an actual count value includes noise, so that determination needsto be performed more carefully. A procedure thereof is illustrated inFIG. 10. FIG. 10 is a flowchart illustrating a signal processingprocedure of the signal processing circuit DS of the three-dimensionalimage element 153.

Here, measurement of a pixel Px(K,j) will be described (refer to S220).The signal processing circuit DS may process the pixels Px(i,j) seriallyor process the pixels Px(i,j) in parallel by providing a plurality ofcalculation circuits. First, count numbers NC1(t) to NCγ(t) are readfrom the buffer memory Bx(j) and stored in a memory of the signalprocessing circuit DS (refer to S221). When a count number of the countnumber NCα(t) is small, noise is not negligible, so that a differenceequal to or less than a noise level ΔN(t) is not able to be regarded asbeing significant (refer to 3222). Though various kinds of noise, suchas dark current noise, 1/f noise, and thermal noise, generally exist,greatest noise in measurement of the number of photons is shot noise.The shot noise proportional to √N normally accompanies the detectednumber of photons N (average value). Thus, it is necessary to considerthat the count number NCα(t) basically has noise proportional to√NCα(t). In particular, in a case where a significantly large signalneeds to be found for the background light, only a signal larger thanthe count number NC1(t) by the noise level ΔN(t)=Δ·√NC1(t) is able to beregarded as a significantly large signal. As a stricter condition,ΔN(t)=A·√NC1(t)+B may be used. In the aforementioned formula, A≥1 andB≥0 (A and B in FIG. 9(b) are unrelated constants). By increasing A,erroneous detection that a signal by the shot noise is erroneouslyregarded as an object is able to be reduced. For reducing such erroneousdetection to a negligible level, A is preferably 3 or more, and morepreferably 4 or more. B is a noise component, such as dark currentnoise, other than the shot noise.

Though NC1(t) that does not include the reflection light of the pulselight but includes only the background light signal is used above todecide the noise level ΔN(t), the noise level ΔN(t) may be decided byanother method. For example, NC2(t) to NCγ(t) are measured withoutmeasuring NC1(t), and on the basis of an average value Ave (NCα(t)) ofNC2(t) to NCγ(t), calculation may be performed as follows:

ΔN(t)=A·√Ave(NCα(t))+B.

In many cases, the number of ones including the reflection light signalof the pulse light among NC2(t) to NCγ(t) is 1 or 2, and most of theminclude only the background light signal. Thus, Ave (NCα(t)) extremelyclose to an average value of the background light. As γ increases, adifference between the average value of the background light signal andAve (NCα(t)) is reduced. Further, from a different point of view, sincethe aforementioned formula evaluates ΔN(t) largely, ΔN(t) is estimatedlargely, thus making it possible to reduce erroneous detection.

However, since a circuit, scale increases and a calculation time becomeslong when a square root is strictly obtained, substitution with anapproximate value is also possible. For example, an approximation methodis also usable in such a manner that, when a most significant bit of thecount number NC1(t) is in a kth digit, the number having a mostsignificant bit in a k/2th digit (rounded up when k is an odd number) orthe number which has a most significant bit in a k/2th digit (rounded upwhen k is an odd number) and whose lower is 1 is set as the noise levelΔN(t).

In algorithm of FIG. 10, a maximum value of the count number NCα(t) issearched for first. In a loop from step S240 to step S244, α indicatingthe maximum value is obtained and a value thereof β is decided. Next,whether or not a difference between a count number NCβ(t) and the countnumber NC1(t) is larger than ΔN is checked (refer to S245). When beingnot larger, it cannot be said that the count number NCβ(t) issignificantly larger than the count number NC1(t), so that a resultindicated by step S256 is obtained as the decision of the distance. Whenthe difference between the count number NCβ(t) and the count numberNC1(t) is larger than ΔN, a larger one of a count number NC(β+1)(t) anda count number NC(β−1)(t) is then selected and a value thereof α isreplaced with (refer to S246 to S248). Next, whether or not a differencebetween a count number NCη(t) and the count number NC1(t) is larger thanΔN is checked (refer to S249). When being not larger, it cannot be saidthat the count number NCη(t) is significantly larger than the countnumber NC1(t), so that a result indicated by step S250 is obtained asthe decision of the distance. Next, in accordance with a magnituderelationship between β and η (refer to S252), a distance and the likeare calculated by formulas of step S253 and step S254. In the foregoingalgorithm, a distance having highest reliability is indicated. A finallyobtained result is stored in a memory as distance information D(K,j),two-dimensional image information (background light signal) G1(K,j), andtwo-dimensional image information (pulse light reflection light signal)G2(K,j) and are output to outside (refer to S251).

In this manner, the signal processing circuit DS has a function ofcalculating and storing the distance information D(K,j) and thetwo-dimensional image information G1(K,j) and G2(K,j) and outputtingthem to the external system 400. However, a specific calculation methodis not limited thereto and various kinds of algorithm are able to beadopted.

In the invention, the pixel storage element Mx(j) is able to perform, inparallel, a function of counting an electrical pulse detecting a photonand a function of reading a counting result. Therefore, there is no casewhere a measurement result is not able to be extracted until signalaccumulation in each row ends, and even in the middle of signalaccumulation in each row, a measurement result is able to be extracted.For example, when a frame frequency is 30 Hz and the number of rows M ofthe pixels of the light receiving unit 154 is 40, a time of 1/1200 secis able to be used for acquisition of data in each of the rows. When apulse light emission cycle is 190 kHz, light emission of 158 pulses isable to be integrated to obtain data of one row. When the object 11 isat a close distance, data is able to be obtained even through lightemission of one pulse in some cases. On the other hand, for the remoteobject 11, data is not able to be obtained unless a lot of data of pulselight emission are integrated. Accordingly, when the measurement resultis obtained in the middle, information about the object 11 close to thethree-dimensional image element 153 is able to be output earlier. Thatis, an object nearest an automobile or robot mounted with thethree-dimensional image element 153 is detected even 1/30 second earlierand an alarm is issued to a control system of the automobile or robot,so that a collision is able to be prevented. A situation where arelative speed to the object 11 at a close distance of several m reaches100 km per hour is difficult to be caused, and in a case of 30 km perhour, even though a moving distance in 1/30 second is about 30 cm andthe time is short, a possibility of avoiding a collision is able to beincreased.

In the two-dimensional image information G1(i,j) and G2(i,j), thetwo-dimensional image information (background light signal) G1(i,j) isby the background light and is useful for recognizing a shape or thelike of the object 11. In particular, in a case where information from anormal image sensor is used in combination, both data are compared sothat the object 11 common in the both data is specified, thus making itpossible to acquire correspondence between the recognition of the object11 and a distance to the object 11. Further, in a case where thedistance is difficult to be specified due to a great difference,proximity of the object 11 is able to be determined by tracing lapse oftime of the two-dimensional image information (pulse light reflectionlight, signal) G2(i,j). That is, when a value of the two-dimensionalimage information (pulse light reflection light signal) G2(i,j)significantly increases, the object 11 of the pixel (i,j) is proximate,and when the value decreases, the object 11 is remote. Thetwo-dimensional image information (pulse light reflection light signal)G2(i,j) may be compared between continuous frames or separate frames orthe comparison may be performed every light emission of multiple orsingle pulse.

The signal processing circuit DS may perform control about by whatprocedure the fan-like pulse light 124 is to be radiated (row selection)and in what order of columns calculation is to he performed for an arrayof the pixels Px(i,j) in m rows and n columns, or may have a memorytherefor. Further, control of a timing when a photon detection signal ofa pixel Px(i,j) is counted may be performed. An example thereof includescontrol in which an activation time of the signal T1 is severalmultiples of an activation time of another signal Tα to measure thesignal of the background light with high accuracy. Moreover, the signalprocessing circuit DS may control a timing when the fan-like pulse light124 is generated or a timing when the pixel Px(i,j) is activated. Forexample, in order to measure the background light described above, thepixel Px(K,j) is activated, the count number is accumulated in thebinary counter BC1 during the time width ΔT1, and when the time widthΔT1 lapses, a signal is transmitted to the pulse light illuminationsystem 110 through the control circuit 160 so as to perform pulse lightemission. Moreover, when the time width ΔT1 lapses, the signal T2 isactivated.

The signal storage processing unit 155 or the control circuit 160 mayhave a memory in which at least the distance information D(i,j) of allthe pixels and the two-dimensional image information G1(i,j) and G2(i,j)are accumulated. These pieces of information obtained by the signalprocessing circuit DS may be sequentially accumulated in the memory, andoutput to the external system 400 through the control circuit 160 inaccordance with a request of the external system 400. Moreover, in acase where the memory even for a plurality of frames is provided,results of comparison between the frames and calculation may be furtheroutput.

(Effect Verification)

In accordance with the invention described above, a test model wascreated and characteristics thereof were evaluated. As the pulse lightillumination system 110, one VCSEL with a peak wavelength of 945 nm wasused as the light emitting element 122 and was driven so that light wasemitted with a pulse peak output of 80 W and a pulse full width at halfmaximum of 5 nsec. For the fan-like light radiation system 123, acollimator lens was used as the collimate light generator 130 andincidence was performed on a MEMS mirror (one-dimensional scanningdevice 131) at an angle of 35 degrees. Laser light reflected in thehorizontal direction was incident on a Powell lens (fan-like beamgenerator 132) with an aperture of 8.9 mm and spread in a fan shape withthe horizontal radiation angle θh=90 degrees. The beam thickness Δθ ofthe laser light (fan-like pulse light 124) output from the Powell lenswas almost 1.5 degrees. A plane of the MEMS mirror is inclined at 45degrees with respect to the horizontal plane and the laser light in thefan shape is radiated in the horizontal direction while no current flowsin the MEMS mirror. When the mirror was caused to oscillate up and downby ±5 degrees from such a state, the laser light was caused to oscillatein the vertical direction by ±10 degrees and almost uniform radiation ina range of the vertical radiation angle θv=20 degrees was realized.Since dispersion of angle setting of the MEMS mirror was ±0.2 degrees,dispersion of an output direction of the laser light was ±0.4 degrees,and a sufficient margin was secured for angle resolution 0.5 degrees forone pixel.

At a distance of 30 m from the pulse light illumination system 110,average radiation intensity of a radiation region was 210 μW/cm² anddispersion in the horizontal direction was ±10% or less. A repetitivelight emission frequency of a laser pulse was 190 kHz in considerationof a condition for a class 1. Image acquisition of 30 frames per secondwas assumed so that data is able to be accumulated for light emission of150 laser pulses to the maximum in one frame.

As the imaging optical system 151 of the light receiving system 140, alens with a focal distance of 4.5 mm, an F-number of 1.8, and aneffective diameter of 2.5 mm was used. Used as the optical band-passfilter 152 was an interference filter for which a central wavelength wasselected so that a peak wavelength of laser and a center value of atransmission band match at a room temperature. About the interferencefilter, as illustrated in FIG. 1, a hemisphere dome made of resin thatis transparent to an infrared ray was provided at the front of theimaging optical system 151 as the protection cover 150, and theinterference filter was formed in an inner surface of the protectioncover 150. A diameter of the hemisphere was 15 mm.

The interference filter had a full width at half maximum of thetransmission band of 10 nm and an average transmittance of 55%. Sincetemperature dependence of the light emission peak wavelength of theVCSEL laser was 0.07 nm/K and the center value of the transmission bandof the interference filter was 0.025 nm/K, a relative deviation betweenthe laser peak wavelength and the center value of the transmission bandof the interference filter was ±2.8 nm at 85° C. to −40° C. Evenincluding the full width at half maximum of the light emission peak ofthe laser of 1 nm, the deviation was within the width of thetransmission band of 10 nm so that usage was enabled without problemseven when no temperature control was performed. It is important that thelight emission peak wavelength of the light emitting element 122 and thecenter value of the transmission band of the optical band-pass filter152 match near a temperature at a center of a temperature zone forusage.

The light receiving unit 154 of the three-dimensional image element 153was constituted by pixels Px(i,j) with a square of 50 μm so as to have7.2 k (7200) effective pixels in total: 180 effective pixels in thehorizontal direction and 40 effective pixels in the vertical direction.An effective part of the light receiving unit 154 is 9 mm×2 mm=18 mm².

In a pixel Px(i,j), seven circular SPADs 180 each having an effectivedetection region with a diameter of 10 μm were arranged as illustratedin FIG. 5. Each of the SPADs 180 is provided with the micro lens 181with a bottom size of 15 μm. A height of the micro lens 181 was about 10μm. A fill factor of the pixel Px(i,j) was 22%. Each of the SPADs 180was operated with the deadtime of 20 nsec. An effective quantumefficiency of the SPAD 180 having the micro lens 181 was 10%. An averageof the number of received photons by the background light, which wasmeasured by placing a white plate whose reflectivity to infrared lightwith a wavelength of 945 nm was 50% at midday of fine weather, was 0.29per 100 nsec in one SPAD 180. Thus, an average of the detected number ofphotons by the background light in all the seven. SPADs 180 was 1.9 per100 nsec. In a case of counting with a pulse having a width of 1.0 nsec,a plurality of photons are detected almost at the same time and apossibility of under count is about 2%, but such a numerical value doesnot greatly affect a counting result.

The signal line Lx(j) connecting each of the pixels Px(i,j) and thecorresponding pixel storage element Mx(j) is arranged between the lightreceiving unit 154 and the signal storage processing unit 155 of thethree-dimensional image element 153. A length thereof is about 2.5 mm.Since a wire delay time depends on the parasitic capacitance of thesignal line Lx(j), no other wire was provided around the signal lineLx(j) in order to minimize the delay time. As a result, the wire delaytime was suppressed to about several tens psec. In addition, a delaytime of the delay circuit 194 of the photon detection signal generationunit 191 of FIG. 7 was set as 100 psec. On the other hand, a delay timeof the delay circuit 199 of the pixel signal output circuit 196 was setas 200 psec.

The image storage element Mx(j) has 42 binary counters BC1 to BC42. Inconsideration of a maximum signal value that can be counted by thebinary counters BC1 to BC42, bits of the respective binary counters BC1to BC42 were differentiated from 11 bits to 6 bits. The binary countersBC1 to BC7 had 11 bits, the binary counters BC8 to BC10 had 10 bits, thebinary counters BC11 to BC14 had 9 bits, the binary counters BC15 toBC21 had 8 bits, the binary counters BC22 to BC28 had 7 bits, and thebinary counters BC29 to BC42 had 6 bits. It is easy to designarrangement of binary counters all of which have the same number of bitsOn the other hand, by adjusting the number of bits for each of thebinary counters BC1 to BC42 as described above, there is an effect ofcapable of reducing an area of the pixel storage element Mx(j) by 25% to28%. A total number of outputs from the binary counters BC1 to BC42 is332. Since it is difficult to constitute the column signal line C(j) by332 signal lines by parallel wiring, the column signal line C(j) isconstituted by 11 signal lines and data is sequentially read for each ofthe binary counters BC1 to BC42. Selection of the binary counter BCα isperformed when the memory selection circuit 163 activates the memoryselection line Rm(α). The memory selection circuit 163 sequentiallyselects memory selection lines Rm(1) and Rm(2) to Rm(γ), and inaccordance with activation of the memory selection lines Rm(1) and Rm(2)to Rm(γ), the output switch 211 sequentially transmits output data ofthe corresponding binary counters BC1 and BC2 to BCγ to the columnsignal line C(j). It is also possible to shorten a reading time byfurther increasing the number of signal lines of the column signal lineC(j) and performing reading of a plurality of binary counters among thebinary counters BC1 to BC42 at the same time.

The signal processing circuit DS was formed by only one calculationcircuit to reduce a circuit scale. The signal processing circuit DS wasconstituted by a 12-bit microcomputer or the like that is used to accessdata of the binary counters BC1 and BC2 to BC42 stored in the buffermemory Bx(j) and perform distance calculation or the like. By using themicrocomputer, algorithm used for distance extraction is able to bechanged. By using the microcomputer with the number of bits (in thiscase, 11 bits) equal to or more than a maximum value of the numbers ofbits of the binary counters BC1 to BC42, a speed of the distanceextraction is able to be enhanced and the distance extraction of allpixels in one row is able to be performed in a time (about 5 μsec)during pulse light emission. When an existing microcomputer is used, atime period for design is shortened, but an area of the signalprocessing circuit DS increases and cost increases. Therefore, in orderto reduce the area of the signal processing circuit DS and reduce cost,it is also possible to design a dedicated circuit.

The signal processing circuit DS has a memory (230 kb) with a capacityof 32 bits for each of the pixels. Thereby, accuracy of distanceinformation D(K,j) is able to be improved by accumulating thetwo-dimensional image information (pulse light reflection light signal)G2(i,j) among frames, and by storing an integrated value thereof andcomparing the integrated value to another measurement value orintegrated value, approach and separation are able to be detected.

In a case of layout with 0.13 μm process, the area of the signalprocessing circuit DS was 2 mm×2 mm, the area of the pixel storageelement Mx(j) was 50 μm×50 μm, an area of the buffer memory Bx(j) was 50μm×40 μm, and a size of the three-dimensional image element 153 was 10mm×4.5 mm. A non-volatile memory in which the algorithm for distanceextraction and an operation condition such as scanning order of thepixel storage element Mx(j) are stored is also incorporated.

By using the present optical radar device 100, a measurable range waschecked under three conditions of fine weather, cloudy weather, andnighttime by using a white plate whose reflectivity to infrared lightwith a wavelength of 945 nm was 50% as the object 11. In daytime of fineweather, by integrating radiation of pulse light 150 times, the object11 up to a distance of 30 m between the three-dimensional image element153 and the object 11 was able to be captured. Measurement dispersion ina vicinity of the distance of 30 m was about 0.5 m. A relationship ofthe measurement dispersion and error to a distance is illustrated inFIG. 11. FIG. 11 is a graph illustrating a measurement error andmeasurement dispersion of the three-dimensional image element 153. InFIG. 11, a horizontal axis indicates an actual distance (unit: m)between the three-dimensional image element 153 and the object 11 and avertical axis indicates an error (unit: m) of a measurement value of theactual distance. As illustrated by circles in FIG. 11, as the actualdistance is short, the error is reduced. However, when the actualdistance is 6 m or less, the error increases as illustrated by squares.This is because radiation intensity of the pulse light is high at aclose distance so that the SPAD 180 is saturated comparatively anddetection efficiency is lowered. Note that, a square portion indicatesan error by which the distance is determined shortly and is not an errorof recognizing a close object to be remote or a hazardous measurementresult.

In cloudy weather, unless the other conditions were not changed, theerror when the actual distance was in the vicinity of 30 m was improvedto 15 cm. Similarly, in nighttime, the error was improved to 5 cm. Evenin a case where it is difficult to monitor the surroundings by a normalcamera video because a surrounding area is dark, for example, innighttime, three-dimensional information of the surroundings, which alsoincludes the distance information D(K,j), is able to be collected by thethree-dimensional image element 153.

The present optical radar device 100 was installed at height of 60 cmfrom a road surface, a central optical axis defined by theone-dimensional scanning device 131 was matched with a horizontal plane,scanning was performed at an angular step of 0.5 degrees from 0 degreesto −10 degrees as a scanning angle of laser light relative to thehorizontal plane, and then scanning was performed similarly at anangular step of 0.5 degrees from +0.5 degrees to +10 degrees. Throughfirst measurement at 0 degrees, one positioned at height of 60 cm fromthe road surface, other than one whose reflectivity of an infrared raywas significantly low, was able to be detected when the distance betweenthe three-dimensional image element 153 and the object 11, which was alongest measurement distance of the optical radar device 100, was within30 m. Thereby, an object which is an obstacle to traveling of a vehicleand a pedestrian including a child is also able to be detected by firstmeasurement of one frame. In a case where the scanning angle shifts to aminus side, when the angle reaches −1.5 degrees (first numerical valueof the step of 0.5 degrees, which exceeds Arctan(0.6 m/30 m)), laserlight hits the road surface within the distance of 30 m and detection ofthe road surface starts. At the angle of −10 degrees, the laser lighthits the road surface at the distance of 3.5 m (=0.6 m/tan 10 degrees),so that a situation of the road surface within the distance of 30 m to3.5 m is able to be observed. For example, a rock, a tree, a fallingobject, an animal, a carcass of an animal, a hole formed on the roadsurface, or the like, which is an obstacle to traveling of a vehicle, isable to be detected, so that utilization for risk avoidance is enabled.In scanning in which the angle is from +0.5 degrees to +10 degrees, atree protruding on the road, a sign that is tilted, further, a loadextending onto the road from a truck bed, or the like, at height of upto 5.28 m (=30 m×tan 10 degrees) is able to be detected, so thatutilization for risk avoidance is enabled. The installation position andthe scanning order of the optical radar device 100 are able to beappropriately selected in accordance with priority order in whichvarious obstacles as described above are observed.

Embodiment 2

The present embodiment is the same as Embodiment 1 other than adifference that in measurement of each line (row), pulse light isradiated by changing power thereof in two stages so that a part at aclose distance is firstly measured through radiation with low power anda whole is then measured with high power.

As described in Embodiment 1, the intensity of the pulse light is toohigh at the close distance and the light receiving system 140 issaturated so that correct distance measurement is not able to beperformed. Thus, the intensity of the pulse light is firstly reduced to10 W and integration measurement is performed ten times, and then,integration is performed 140 times with the power of 75 W similarly toEmbodiment 1. After the integration for the first ten times, dataaccumulated in the pixel storage element Mx(j) is copied to the buffermemory Bx(j) and data processing is performed for the data in the buffermemory Bx(j). Distance data that is obtained is stored in the memory ofthe signal processing circuit DS. A result of performing measurement 140times with high power may be directly integrated to a result ofperforming integration first 10 times with low power. Signal processingis performed similarly to Embodiment 1 for the pixel storage elementMx(j) in which final integration is performed.

Here, two types of signal processing results for the lower power and thehigh power are generated. Distance information D(i,j)l and distanceinformation D(i,j)h are provided as the distance signal, two-dimensionalimage information G1(i,1 )l and two-dimensional image informationG1(i,j)h are provided as the two-dimensional image information G1(i,j),and two-dimensional image information G2(i,j)l and two-dimensional imageinformation G2(i,j)h are provided as the two-dimensional imageinformation G2(i,j). They are preferably selected as follows.

Distance signal: D(i,j)=D(i,j)l (D(i,j)l≤6 m)

-   -   D(i,j)=D(i,j)h (D(i,j)l>6 m)

Background light signal: G1(i,j)=G1(i,j)h

Pulse light reflection light signal: G2(i,j)=MAX (G2(i,j)h,G2(i,j)l×106)

6 m that is a determination criterion of the distance signal is to bechanged depending on an operation condition of the optical radar device100. A distance at which the light receiving system 140 starts to besaturated may be a determination distance. Since the background light isnot related to the intensity of the pulse light, a final integrationresult may be used. In the pulse light reflection light signal, when thedistance is close, the two-dimensional image information (pulse lightreflection light signal) G2(i,j)h does not indicate correct signalintensity because of the saturation of the light receiving system 140,and therefore, for such a part, the measurement result of the lowerpower is to be used by converting a difference of the power intensityand the number of times of integration. This means that X or Y that islarger is selected in MAX (X,Y). A conversion coefficient of 106(=(140×75 W+10×10 W)/(10×10 W)) is a ratio of a total amount of radiatedpulse light in measurement with the high power and measurement with thelow power in the example described above, and is to be changed dependingon an operation condition of the optical radar device 100.

As a result, even when the distance between the three-dimensional imageelement 153 and the object 11 is close to be from about 3 m to 0.75 m,the distance was able to be measured correctly. Measurement dispersion(error described above) at the distance of 3 m was about 15 cm. At, thedistance of 1.5 m or less, an effect of saturation was seen, but theeffect was about 10 cm.

By switching the power of the pulse light as described above,measurement from the close distance to the long distance is able to beperformed with high accuracy. The present method is excellentparticularly in that the object 11 at the close distance is able to bedetected in an early stage of starting one frame without waiting for anend of one frame.

Embodiment 3

FIG. 12 is a schematic view of the three-dimensional image element 153according to the present embodiment. FIG. 13 is a schematic viewillustrating connection of the pixel Px(i,j), signal lines Lxa(j) toLxC(j), and pixel storage elements Mxa(j) to MxC(j) of thethree-dimensional image element 153 according to the present embodiment.

A substantial difference of the present embodiment from Embodiment 1 isthat a plurality of pixel storage elements Mx(j) are provided so thatdata of a plurality of pixels that are adjacent is able to be measuredat the same time. In an example of FIG. 12, each column has three pixelstorage elements Mxa(j), Mxb(j), and MxC(j). In a case where accuracy ofangle control of the one-dimensional scanning device 131 is low andcorrespondence between fan-like pulse light 124-α and a pixel Px(α,j) isdisturbed, the beam thickness Δθ is inevitably increased to increase amargin in the configuration of Embodiment 1. However, this causesreduction of the radiation intensity of the pulse light at the object11. Alternatively, it becomes necessary to use the light emittingelement 122 with higher output. This results in lowering of detectionsensitivity or cost increase. In the present embodiment, the beamthickness Δθ is kept small and the light radiation intensity isincreased, and angle dispersion of the one-dimensional scanning device131 is able to be covered by observing adjacent pixels Px(i,j) at thesame time. Thus, in the present embodiment, by relaxing specificationrelated to the one-dimensional scanning device 131, cost thereof is ableto be reduced. Though the three pixel storage elements Mxa(j), Mxb(j),and MxC(j) are provided in each column in the present embodiment, thenumber thereof may be two or four or more.

The pulse light illumination system 110 of the present embodiment hasthe changed collimate light generator 130 and a reduced beam thicknessΔθ of 0.5 degrees, but is the same as that of Embodiment 1 in theothers. The light receiving system 140 is the same as that of Embodiment1 other than that a configuration of the three-dimensional image element153 is different. In the light receiving unit 154, as illustrated inFIG. 13, in order to connect three pixels Px(i−1,j), Px(i,j), andPx(i+1,j) adjacent in a row direction to the three pixel storageelements Mxa(j), Mxb(j), and Mxc(j), the row selection line is alsoincreased to three row selection lines Ra(j), Rb(j), and Rc(j) and thesignal line is also increased to three signal lines Lxa(j), LXb(j), andLxc(j). The signal lines Lxa(j), LXb(j), and Lxc(j) are respectivelyconnected to the pixel storage elements Mxa(j), Mxb(j), and Mxc(j). Asswitches that supply outputs of pixel signal output circuits 196 of therespective pixels(i,j) to the signal lines Lxa(j), LXb(j), and Lxc(j),row selection switches 201 a, 201 b, and 201 c are provided and the rowselection switches 201 a, 201 b, and 201 c are respectively opened orclosed by the row selection lines Ra(i), Rb(i), an Rc(i). For example,in a case where the pixels Px(i−1,j), Px(i,j), and Px(i+1,j) areselected, the row selection circuit 161 controls all row selection linesRa(i) so that row selection lines Ra(i−1), Rb(i), and Rc(i+1) areactivated (Vcc in FIG. 13) and the others are deactivated (0 V in FIG.13). Thereby, observation data of the pixel Px(i−1,j) is accumulated inthe pixel storage element Mxa(j), observation data of the pixel Px(i,j)is accumulated in the pixel storage element Mxb(j), and observation dataof the pixel Px(i+1,j) is accumulated in the pixel storage elementMxC(j).

The pieces of observation data of the pixel storage elements Mxa(j),Mxb(j), and MxC(j) are copied to buffer memories Bxa(j), Bxb(j), andBxC(j) through column signal lines Ca(j), Cb(j), and Cc(j),respectively. The memory selection circuit 163 that selects the binarycounters BC1 to BCγ of each of pixel storage elements Mxα(j) when dataof a pixel storage element Mxα(j) is transferred to a buffer memoryBxα(j) through a column signal line Cα(j) has substantially nodifference from that of Embodiment 1. It may be considered that threecircuits which are the same are arranged in parallel. A memory selectionline Rmα(β) that drives the output switch 211 of each of the pixelstorage elements Mxα(j) also has substantially no difference from thatof Embodiment 1. Since all are processed in parallel, amounts of thepixel storage element and the buffer memory increase, but a timerequired for measurement is not elongated or a frame frequency is notreduced.

Various kinds of algorithm are applicable to a method of extracting thedistance information D(i,j) and the two-dimensional image informationG1(i,j) and G2(i,j) from the pieces of data copied to the buffermemories Bxa(j), Bxb(j), and BxC(j). A simplest example will bedescribed below. FIG. 14 is a flowchart illustrating a signal processingprocedure of the signal processing circuit DS of the three-dimensionalimage element 153 according to the present embodiment. The processingprocedure illustrated in FIG. 14 has basically the same content as thatof FIG. 10. That is, the pieces of data of the buffer memories Bxa(j),Bxb(j), and BxC(j) are respectively read as count numbers NC1α(t),NC2α(t), and NC3α(t) (S301), a maximum value is found from among them(S302 to S311), the value is used as a count number NCfβ(t) to decide anoise level from a count number NCf1(t) (S320), and distance informationD(t) and a pulse light reflection light signal IC(t) are decided fromthe count number NCfβ(t), a count number NCf(β−1)(t), or a count numberNCf(β+1)(t) (S321 to S370). In a case of f=2, D(K,j)=D(t) andG2(K,j)=IC(t) are provided, in a case of f=1, D(K−1,j)=D(t) andG2(K−1,j)=IC(t) are provided, and in a case of f=3, D(K+1,j)=D(t) andG2(K+1,j)=IC(t) are provided. The same is also applied to a case of thetwo-dimensional image information G1(K,j) (refer to S381). Step S380 isprovided to prevent that a value that has been already measured isoverwritten in a specific case where a variation of the one-dimensionalscanning device 131 is great and two successive scanning angles arereversed.

In a case where the beam thickness Δθ is 0.5 degrees and the pixel angleresolution is 0.5 degrees, even when the fan-like pulse light 124 hasdispersion of ±0.83 degrees to the maximum, at least 34(=(0.5×2−0.83)/0.5) % of a light amount is radiated onto the object 11corresponding to any of the pixels Px(i,j) so that a sufficient signalamount is able to be secured. In Embodiment 1, the beam thickness Δθ is1.5 degrees and three times as large as that of the present embodiment,and when a laser with the same output is used, the radiation intensityof the pulse light at the object 11 in the present embodiment is threetimes larger, so that an equivalent minimum light amount (34%×3=102%) isable to be realized in a margin of ±0.83 degrees. An angle margin of thefan-like pulse light 124 in Embodiment 1 is ±0.4 degrees and an anglemargin almost twice the angle margin is able to be secured in thepresent embodiment.

Embodiment 4

FIG. 15 is a schematic view illustrating a configuration of the fan-likelight radiation system 123 according to the present embodiment. Thepresent embodiment is the same as Embodiment 1 other than that theconfiguration of the fan-like light radiation system 123 that is a partof the pulse light illumination system 110 is different.

The fan-like light radiation system 123 in the present embodiment isillustrated in FIG. 15. A difference from the fan-like light radiationsystem 123 of Embodiment 1 is that the fan-like beam generator 132 that,after the collimate light generator 130 shapes light from the lightemitting element 122 into almost parallel spot light 133 (in the Y-Zplane), makes the spot light 133 spread in the fan shape is arranged sothat the one-dimensional scanning device 131 uses the light spread inthe fan shape to perform scanning in the vertical direction (Ydirection). An advantage of the present configuration is that anincidence angle of the light on the fan-like bean generator 132 isalways fixed, so that intensity distribution in the horizontal directionand the vertical direction of the fan-like pulse light 124 has lessdispersion in the target field of view 10. The present embodiment has anadvantage that, in a case where the Powell lens is used as the fan-likebeam generator 132, when an incidence angle on the Powell lens changes,the horizontal radiation angle θh and/or the beam thickness Δθ slightlychange/changes due to a deflection angle in the vertical direction, butsuch a change is not generated. As a result, it is possible to increaseuniformity of the fan-like pulse light 124, increase pulse lightradiation intensity at the object 11, and widen a measurement range.

The one-dimensional scanning device 131 is also able to use a MEMSmirror element similarly to Embodiment 1, but uses a polygon mirror inFIG. 15. Differently from Embodiment 1, pulse light is spread in the fanshape in front of the one-dimensional scanning device 131 so that alarger reflection plane than that of Embodiment 1 is required, and apolygon mirror is more advantageous in terms of cost in some cases. Thecontrol circuit 160 controls a rotation angle of the polygon mirror andperforms synchronous control of the angle of the mirror and the lightreceiving system 140 so that a signal from the object 11 irradiated withthe fan-like pulse light 124 is able to be detected.

Embodiment 5

FIG. 16 is a schematic view illustrating a configuration of the lightemitting element 122 and the fan-like light radiation system 123according to the present embodiment. The present embodiment is the sameas Embodiment 1 other than that the configuration of the light emittingelement 122 and the fan-like light radiation system 123 that are a partof the pulse light illumination system 110 is different.

FIG. 16 illustrates the light emitting element 122 and the fan-likelight radiation system 123 in the present embodiment. A difference fromEmbodiment 1 is that a fan-like laser light source 134 that emits thefan-like pulse light 124 is arranged in one or more planes of a rotatingbody (with an X-axis as a rotational axis) that is the one-dimensionalscanning device 131. The fan-like laser light source 134 is, forexample, a combination of a laser light source (light emitting element122), a collimate lens (collimate light generator 130), and a Powelllens (fan-like beam generator 132). Alternatively, one in which manylaser chips are linearly arrayed to perform light emission at the sametime may be used. In the one-dimensional scanning device 131, one ormore fan-like laser light sources 134 as described above are arrangedaround the rotational axis so that a scanning angle in the verticaldirection is able to be controlled by control of a rotation angle.

An advantage of the present configuration is that the pulse lightillumination system 110 is able to be reduced in size by simplifyingarrangement of a light path.

Embodiment 6

A difference of the optical radar device 100 of the present embodimentfrom those of the foregoing embodiments is that a sensor that measures adistance to the object 11 by a ToF (Time-of-flight) system is mountedinstead of the three-dimensional image element 153 that constitutes thelight receiving system 140. The three-dimensional image element 153 ofEmbodiment 1 is not essential for providing an advantage that the fieldof view 10 in a rectangular shape is scanned with the fan-like pulselight 124 that is spread in a long-side direction so that the object 11such as a pedestrian or an obstacle is found at an initial stage ofscanning where scanning of the whole of the field of view 10 is notcompleted. For example, a circuit in which the signal storage processingunit 155 performs signal processing by a TCSPC system while using a SPADarray like the light receiving unit 154 of the three-dimensional imageelement 153 of Embodiment 1 may be used. A system in which the lightreceiving unit 154 drives an avalanche photodiode not in a Geiger modebut in a current amplification mode and the signal storage processingunit 155 detects an increase or decrease of a signal current transmittedfrom each of the pixels Px(i,j) of the light receiving unit 154 tothereby measure a flight time may be provided. In any system, the lightreceiving unit 154 has pixels arranged in a two-dimensional array so asto cover the target field of view 10 and the signal storage processingunit 155 has a flight time measurement circuit corresponding to a groupof pixels in one row arranged in a long-side direction of thetwo-dimensional array.

It should be understood that embodiments and examples disclosed hereinare illustrative and non-restrictive in every respect. The scope of theinvention is defined by the scope of the claims, rather than thedescription above, and is intended to include meaning equivalent to thescope of claims and all modification falling in the scope.

CONCLUSION

A three-dimensional image element according to an aspect 1 of theinvention includes: a light receiving unit in which pixels eachincluding an avalanche photodiode (SPAD 180) that detects light in aGeiger mode are arranged in a two-dimensional matrix pattern; a pixelstorage element to which an electrical pulse is supplied from each ofpixels that constitute a column of the pixels; and a signal processingcircuit that reads data accumulated by the pixel storage element andacquires, for each of the pixels, at least distance informationindicating a distance to an object, in which the pixel storage elementhas a plurality of binary counters that integrate the number ofelectrical pulses at mutually different timings, and the reading of thedata by the signal processing circuit is able to be performed inparallel with the integration.

According to the aforementioned configuration, since the pixel storageelement is able to be realized with a small area, many pixel storageelements are able to be mounted in the three-dimensional image elementand many pieces of image information are able to be processed at a time.Further, the signal processing circuit is able to acquire a progressionof a count of the number of electrical pulses. Accordingly, it ispossible to detect an object at a close distance in a wide field of viewand detect the distance before a final result of counting the number ofelectrical pulses is acquired.

In the three-dimensional image element according to an aspect 2 of theinvention, the number of columns of the pixels in the light receivingunit is larger than the number of rows of the pixels in the lightreceiving unit, in the aspect 1.

According to the aforementioned configuration, in an environment thereare many objects that are wide in a row direction, by acquiring data ofa first one or several rows, an object in a wide field of view coveredby many columns is able to be detects, thus making it possible to detectthe object at high speed and with high probability.

In the three-dimensional image element according to an aspect 3 of theinvention, the light receiving unit, the pixel storage element, and thesignal processing circuit are formed on a silicon substrate in amonolithic manner, in the aspect 1 or 2.

According to the aforementioned configuration, by manufacturing thelight receiving unit, the pixel storage element, and the signalprocessing circuit as one chip, the three-dimensional image element thathas high accuracy and high reliability is able to be produced at lowcost.

In the three-dimensional image element according to an aspect 4 of theinvention, each of the pixels includes a plurality of avalanchephotodiodes that detect light in a Geiger mode, in any of the aspects 1to 3.

According to the aforementioned configuration, when the pixel includesthe plurality of avalanche photodiodes, lowering of detection efficiencydue to a deadtime (lowering of detection efficiency resulting from thata next photon is able to be detected after a certain photon is detected)is able to be prevented. Accordingly, according to the aforementionedconfiguration, measurement sensitivity of the three-dimensional imageelement is able to be enhanced. In particular, an object at a closedistance has a large signal amount and accuracy of distance measurementis deteriorated because of lowering of the detection efficiency due tothe deadtime, so that the accuracy of distance measurement at the closedistance is able to be improved by the aforementioned configuration.

In the three-dimensional image element according to an aspect 5 of theinvention, the number of bits of a digital signal processed by thesignal processing circuit is equal to or more than a maximum number ofoutput bits of each of the plurality of binary counters, in any of theaspects 1 to 4.

According to the aforementioned configuration, calculation processing issimplified and a result is able to be obtained with a small number ofsteps, thus making it possible to reduce a processing time and powerconsumption.

An optical radar device according to an aspect 6 of the inventionincludes the three-dimensional image element according to any one of theaspects 1 to 5, and the optical radar device includes: a pulse lightillumination system that has a light emitting element that emits pulselight, an optical scanning unit (one-dimensional scanning device 131)that performs scanning with the pulse light in a direction parallel to afirst plane, and an optical conversion unit (fan-like beam generator132) that converts the pulse light into fan-like pulse light that isspread in a direction vertical to the first plane; and an imagingoptical system that images and projects light, which is from at least apart of a region to which light is radiated from the pulse lightillumination system, onto the light receiving unit of the threedimensional image element through an optical band-pass filter.

According to the aforementioned configuration, it is possible to performradiation from one end to the other end in the direction vertical to thefirst plane all at once (all pixels in the same row are to receivelight), so that a radiation range of each unit radiation is able to bewidened. Further, the aforementioned configuration makes it possible tokeep high light radiation intensity as compared to that ofsingle-radiation type.

In the optical radar device according to an aspect 7 of the invention, aspread angle (horizontal radiation angle θh) of the fan-like pulse lightin a fan plane is greater than an angle (vertical radiation angle θv) ofthe scanning, in the aspect 6.

According to the aforementioned configuration, in an environment wherethere are many objects that are wide in a direction vertical to a fanplane, the object is able to be detected at high speed and with highprobability.

In the optical radar device according to an aspect 8 of the invention,the first plane is a plane including a vertical line (Y axis), in theaspect 6 or 7.

Since most objects on land mainly extend upwardly from a ground, byusing fan-like pulse light that is spread in a horizontal plane, theobject is able to be detected at high speed and with high probabilitywithout waiting for scanning of a whole of a target field of view. Thus,according to the aforementioned configuration, it is possible to sensedanger at an earlier stage in usage on land.

In the optical radar device according to an aspect 9 of the invention, atime width in which at least one of the binary counters of thethree-dimensional image element integrates the number of electricalpulses is almost identical with a pulse width of the pulse light orshorter than the pulse width of the pulse light, in any of the aspects 6to 8.

According to the aforementioned configuration, when the time width formeasurement and the pulse width are almost the same, it is possible toimprove an SN ratio of a signal while enhancing time resolution byincreasing power of the pulse light in an allowable range.

In the optical radar device according to an aspect 10 of the invention,at least one of the binary counters of the three-dimensional imageelement integrates the number of electrical pulses before light emissionof the pulse light, in any of the aspects 6 to 9.

According to the aforementioned configuration, it is possible toeliminate an effect of the pulse light to the maximum in measurement ofintensity of background light. Further, according to the aforementionedconfiguration, by measuring the intensity of the background light over alonger time than a measurement time after light emission of the pulselight, a noise level of the intensity of the background light is able tobe reduced. Thus, according to the aforementioned configuration,measurement accuracy of the intensity of the background light isenhanced and a variation of a measurement result is reduced.

In the optical radar device according to an aspect 11 of the invention,the three-dimensional image element is able to output, in addition tothe distance information, an intensity signal of reflection lightobtained when radiation light from the pulse light illumination systemis reflected by the object and an intensity signal of light that doesnot include the reflection light, in any of the aspects 6 to 10.

In the optical radar device according to an aspect 12 of the invention,the optical radar device has a function of storing order of thescanning, causing the optical scanning unit to perform scanning with thepulse light in accordance with the stored order, and synchronouslyperforming reading on the pixels in a corresponding row, in any one ofthe aspects 6 to 11.

According to the aforementioned configuration, scanning is performedfrom a part where an object at issue is likely to be detected dependingon use, and it is not necessary to instruct scanning order from anexternal system for each frame, so that control of the optical radardevice is able to simplified.

An optical radar device according to an aspect 13 of the inventionincludes: a pulse light illumination system that has a light emittingelement that emits pulse light, an optical scanning unit that performsscanning with the pulse light in a direction parallel to a first plane,and an optical conversion unit that converts the pulse light intofan-like pulse light that is spread in a direction vertical to the firstplane; and an imaging optical system that images and projects light,which is from at least a part of a region to which light is radiatedfrom the pulse light illumination system, onto a light receiving unit ofa sensor, which measures at least a distance to an object, through anoptical band-pass filter.

According to the aforementioned configuration, a small-sized pulse lightillumination system capable of scanning a wide range with linear pulselight having high intensity is able to be realized. Further, when amaterial or a circuit other than the three-dimensional image elementaccording to an aspect of the invention is used as a sensor, ameasurement range is able to be widened to a remote range by using alight emitting element and a light receiving element for light with along wavelength to achieve lower intensity of background light.

In the optical radar device according to an aspect 14 of the invention,a spread angle of the fan-like pulse light in a fan plane is greaterthan an angle of the scanning, in the aspect 13.

According to the aforementioned configuration, in an environment wherethere are many objects that are wide in a direction vertical to the fanplane, the object is able to be detected at high speed and with highprobability.

The invention is not limited to each of the embodiments described above,and may be modified in various manners within the scope indicated in theclaims and an embodiment achieved by appropriately combining technicalmeans disclosed in different embodiments is also encompassed in thetechnical scope of the invention. Further, by combining the technicalmeans disclosed in each of the embodiments, a new technical feature maybe formed.

REFERENCE SIGNS LIST

10 target field of view

100 optical radar device

110 pulse light illumination system

120 illumination system power source

121 light emitting element driving circuit

122 light emitting element

123 fan-like light radiation system

124 fan-like pulse light

130 collimate light generator

131 one-dimensional scanning device (optical scanning unit)

132 fan-like beam generator optical conversion unit)

133 spot light

134 fan-like laser light source

140 light receiving system

141 light receiving system power source

150 protection cover

151 imaging optical system

152 optical band-pass filter

153 three-dimensional image element

154 light receiving unit

155 signal storage processing unit

160 control circuit

161 row selection circuit

163 memory selection circuit

170 package

171 lid glass

172 atmosphere

180 SPAR (avalanche photodiode)

181 micro lens

182 metal shield

183 silicon substrate

184 p⁺ diffusion layer

185 n-type diffusion layer

190 SPAD control unit

191 photon detection signal generation unit

192 first inverter

193 second inverter

194 delay circuit

195 NOR circuit

196 pixel signal output circuit

197 signal line driving circuit

198 signal line reset circuit

199 delay circuit

200 signal line pull-down circuit

201, 201 a, 201 b, 201 c row selection switch

210 time switch

211 output switch

400 external system

Px(i,j) pixel

Mx(j), Mxa(j), Mxb(j), Mxc(j) pixel storage element

Bx(j), Bxa(j), Bxb(j), Bxc(j) buffer memory

Lx(j), Lxa(j), Lxb(j), Lxc(j) signal line

R(i), Ra(i), Rb(i), Rc(i) row selection line

Rm(α), Rma(α), Rmb(α), Rmc(α) memory selection line

C(j), Ca(j), Cb(j), Cc(j) column signal line

DS signal processing circuit

S1, S2 to Sγ signal line switching transistor

T1, T2 to Tγ storage element switching signal

BC1, BC2 to BCγ binary counter

ΔT light emission time (full width at half maximum) of pulse light

ΔT1, ΔT2 to ΔTγ time width in which signal line switching transistor isturned on

NC1(t), NC2(t) to NCγ(t) count value of each binary counter at time t,NC11(t), NC12(t) to NC1γ(t) count value of binary counter of Bxa(j) attime t

NC21(t), NC22(t) to NC2γ(t) count value of binary counter of Bxb(j) attime t

NC31(t), NC3(t) to NC3γ(t) count value of binary counter of Bxc(j) attime t

1. A three-dimensional image element comprising: a light receiving unitin which pixels each including an avalanche photodiode that detectslight in a Geiger mode are arranged in a two-dimensional matrix pattern;a pixel storage element to which an electrical pulse is supplied fromeach of the pixels that constitute a column of the pixels; and a signalprocessing circuit that reads data accumulated by the pixel storageelement and acquires, for each of the pixels, at least distanceinformation indicating a distance to an object, wherein the pixelstorage element has a plurality of binary counters that integrate thenumber of electrical pulses at mutually different timings, and thereading of the data by the signal processing circuit is able to beperformed in parallel with the integration.
 2. The three-dimensionalimage element according to claim 1, wherein the number of columns of thepixels in the light receiving unit is larger than the number of rows ofthe pixels in the light receiving unit.
 3. The three-dimensional imageelement according to claim 1, wherein the light receiving unit, thepixel storage element, and the signal processing circuit are formed on asilicon substrate in a monolithic manner.
 4. The three-dimensional imageelement according to claim 1, wherein each of the pixels includes aplurality of avalanche photodiodes that detect light in a Geiger mode.5. The three-dimensional image element according to claim 1, wherein thenumber of bits of a digital signal processed by the signal processingcircuit is equal to or more than a maximum number of output bits of eachof the plurality of binary counters.
 6. An optical radar device thatincludes the three-dimensional image element according to claim 1, theoptical radar device comprising: a pulse light illumination system thathas a light emitting element that emits pulse light, an optical scanningunit that performs scanning with the pulse light in a direction parallelto a first plane, and an optical conversion unit that converts the pulselight into fan-like pulse light that is spread in a direction verticalto the first plane; and an imaging optical system that images andprojects light, which is from at least a part of a region to which lightis radiated from the pulse light illumination system, onto the lightreceiving unit of the three-dimensional image element through an opticalband-pass filter.
 7. The optical radar device according to claim 6,wherein a spread angle of the fan-like pulse light in a fan plane isgreater than an angle of the scanning
 8. The optical radar deviceaccording to claim 6, wherein the first plane is a plane including avertical line.
 9. The optical radar device according to claim 6, whereina time width in which at least one of the binary counters of thethree-dimensional image element integrates the number of electricalpulses is almost identical with a pulse width of the pulse light orshorter than the pulse width of the pulse light.
 10. The optical radardevice according to claim 6, wherein at least one of the binary countersof the three-dimensional image element integrates the number ofelectrical pulses before light emission of the pulse light.
 11. Theoptical radar device according to claim 6, wherein the three-dimensionalimage element is able to output, in addition to the distanceinformation, an intensity signal of reflection light obtained whenradiation light from the pulse light illumination system is reflected bythe object and an intensity signal of light that does not include thereflection light.
 12. The optical radar device according to claim 6,wherein the optical radar device has a function of storing order of thescanning, causing the optical scanning unit to perform scanning with thepulse light in accordance with the stored order, and synchronouslyperforming reading on the pixels in a corresponding row.
 13. An opticalradar device comprising: a pulse light illumination system that has alight emitting element that emits pulse light, an optical scanning unitthat performs scanning with the pulse light in a direction parallel to afirst plane, and an optical conversion unit that converts the pulselight into fan-like pulse light that is spread in a direction verticalto the first plane; and an imaging optical system that images andprojects light, which is from at least a part of a region to which lightis radiated from the pulse light illumination system, onto a lightreceiving unit of a sensor, which measures at least a distance to anobject, through an optical band-pass filter.
 14. The optical radardevice according to claim 13, wherein a spread angle of the fan-likepulse light in a fan plane is greater than an angle of the scanning 15.The optical radar device according to claim 13, wherein the first planeis a plane including a vertical line.
 16. The optical radar deviceaccording to claim 13, wherein the sensor is able to output, in additionto the distance information, an intensity signal of reflection lightobtained when radiation light from the pulse light illumination systemis reflected by the object and an intensity signal of light that doesnot include the reflection light.
 17. The optical radar device accordingto claim 13, wherein the optical radar device has a function of storingorder of the scanning, causing the optical scanning unit to performscanning with the pulse light in accordance with the stored order. 18.The optical radar device according to claim 13, wherein the opticalradar device has a function to measure a distance of an object at aclose distance firstly and then a whole object later.
 19. The opticalradar device according to claim 13, wherein the optical radar device hasa function to measure a distance of an object with reduced intensity ofthe pulse light firstly and then with higher intensity than the reducedintensity later.
 20. The optical radar device according to claim 13,wherein the sensor has a signal storage processing unite in addition tothe light receiving unit, and the signal storage processing uniteincludes a plural of pixel storage elements, a buffer memory, a memoryselection circuit and a signal processing circuit.